Transitions Between Childlessness and First Birth: Three Generations of U.S

Transitions Between Childlessness and First Birth: 2011 Three Generations of U.S. Women August 153 Number 2, Series Copyright information

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Kirmeyer SE, Hamilton BE. Transitions between childlessness and first birth: Three generations of U.S. women. National Center for Health Statistics. Vital Health Stat 2(153). 2011.

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Transitions between childlessness and first birth : three generations of U.S. women. p. ; cm.— (Vital and health statistics. Series 2 ; no. 153) (DHHS publication ; no. (PHS) 2011–1353) ‘‘August 2011.’’ Includes bibliographical references. ISBN-13: 978–0–8406–0646–4 ISBN-10: 0–8406–0646–X 1. Fertility—United States—Statistics. 2. Birth intervals—United States— Statistics. I. National Center for Health Statistics (U.S.) II. Series: Vital and health statistics. Series 2, Data evaluation and methods research ; no. 153. III. Series: DHHS publication ; no. (PHS) 2011–1353. [DNLM: 1. Reproductive Behavior—United States—Statistics. 2. Birth Intervals—United States—Statistics. 3. Fertility—United States—Statistics. 4. Longitudinal Studies—United States—Statistics. W2 A N148vb no.153 2011] HB902.5.U6T73 2011 304.6’320973—dc23 2011017791

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Transitions Between Childlessness and First Birth: Three Generations of U.S. Women

Data Evaluation and Methods Research

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Center for Health Statistics

Hyattsville, Maryland August 2011 DHHS Publication No. (PHS) 2011–1353 National Center for Health Statistics Edward J. Sondik, Ph.D., Director Jennifer H. Madans, Ph.D., Associate Director for Science

Division of Vital Statistics Charles J. Rothwell, M.S., Director Contents

Abstract...... 1 Introduction ...... 1 Methods ...... 1 Data Sources ...... 1 Data Quality...... 2 Analytic Methods ...... 2 Measures ...... 2 Results and Discussion ...... 3 Patterns of First-birth Probabilities (qx)...... 3 Number in Cohort Remaining Childless, by Age (lx)...... 4 Distribution of First Births by Mother’s Age (bx) ...... 4 Expectation of Number of Years to be Childless in the Future (ex)...... 5 Degree of Concentration of First Births...... 6 Importance of Childlessness in the Demographic Context of the 20th Century ...... 7 Trends by Parity Distribution in the 20th Century ...... 7 Cohort TFRs, 1950–2005 ...... 7 Postponement and Recuperation of Fertility ...... 8 Relationship of Childlessness to TFRs...... 9 Conclusion ...... 11 References ...... 11 Appendix. Technical Notes ...... 16

Figures 1. Probability of having a first birth, by age and birth cohort of mother: United States, 1910, 1935, and 1960 ...... 3 2. Cumulative probability of having a first birth, by age and birth cohort of mother: United States, 1910, 1935, and 1960 ...... 4 3. Number of women remaining childless, by age and birth cohort of mother: United States, 1910, 1935, and 1960...... 5 4. Distribution of first births, by age and birth cohort of mother: United States, 1910, 1935, and 1960 ...... 6 5. Average number of years expected to remain childless, by age and birth cohort of mother: United States, 1910, 1935, and 1960 ...... 7 6. Lorenz curves of first births and Duncan Index of Concentration, by birth cohort: United States, 1910, 1935, and 1960 ...... 8 7. Parity distribution at completed fertility of birth cohorts: United States, 1900–1960...... 9 8. Percent distribution of the number of children ever born, by birth cohort of mother: United States, 1910, 1935, and 1960 ...... 10 9. Total fertility rates at completed fertility of birth cohorts: United States, 1950–2005 ...... 10 10. Proportion childless and total fertility rate at completed fertility, by birth cohorts: United States, 1910–1960 ...... 11

iii Text Tables A. Cumulative probability of first birth, by selected age and birth cohort of women: United States, 1910, 1935, and 1960 ...... 4 B. Proportion of women childless, by selected age and birth cohort of women: United States, 1910, 1935, and 1960 ..... 5 C. Mean, median, modal, and maximum number of first births (bx), by birth cohort of women: United States, 1910, 1935, and 1960...... 6 D. Expected number of years childless, by selected age interval and birth cohort of women: United States, 1910, 1935, and 1960 ...... 7 E. Gini Concentration Ratio and Duncan Index of Concentration, by birth cohort of women: United States, 1910, 1935, and 1960...... 8 F. Total fertility rates, by selected age group and birth cohorts of women: United States, 1930, 1940, 1950, 1960, 1970, and 1980 ...... 9

Detailed Tables 1. Maternity table for the 1910 birth cohort, by age of mother ...... 13 2. Maternity table for the 1935 birth cohort, by age of mother ...... 14 3. Maternity table for the 1960 birth cohort, by age of mother ...... 15

Objective This report analyzes the patterns of Transitions Between Childlessness childlessness, and conversely, the first-birth patterns of three birth cohorts and First Birth: Three Generations of American women. For this report, a cohort refers to women born in the same year. The cohorts compared were of U.S. Women women born in 1910, 1935, and 1960—who, consequently, turned 25 by Sharon E. Kirmeyer, Ph.D.; and Brady E. Hamilton, Ph.D., during the Great Depression, the Baby Division of Vital Statistics Boom, and lastly, the post-Baby Boom period. The purpose of the report is to explore the differences in fertility Introduction partners’ availability and intentions, life characteristics of these three course events, subfecundity, and generations of women and to consider unplanned events (1). those differences in light of the social Both the timing of the first birth This report presents three strongly and economic conditions at the time. and the percentage childless have contrasting patterns of childlessness (and profound consequences for society. their complement, descriptions of first Methods These include the demand for schools childbirth) and discusses the context in and housing, as well as the development Life table methodology, including the which these patterns occurred in the probability of having a first birth, the and utilization of women in the labor United States. In addition, this report number of women remaining childless, force. Moreover, the lives of women discusses previously unknown and the expected number of years to who become mothers are significantly relationships between individual remain childless, was applied to each of different from those who do not. To functions of childlessness and the larger the three birth cohorts for comparison. give birth (and to raise a child) results demographic context. Techniques extended from life table in a transition to parenthood, with functions were also used and included immediate and generally permanent measures of first-birth concentration as implications (1). In industrialized well as comparisons between child Methods societies, parenthood affects the lessness and the total fertility rate (TFR). acquisition of material goods (such as Data were based on the Centers for choice of place of residence, housing Disease Control and Prevention’s Data Sources National Center for Health Statistics type, and consumable goods) (2). When tables on cohort fertility. and if women become mothers, they can The patterns of childlessness encounter opportunity costs (for examined in this report used U.S. birth Results example, those that limit education, the cohort data, not period data. A birth ability to work full-time, the possibility cohort for this report is a group of Of the three birth cohorts studied, the women born in 1910 had the to obtain higher professional attainment, women born in the same year and who highest proportion childless and a low promotions, and higher incomes) (3). share the same general or common TFR. In contrast, the women born in In nonindustrialized societies, rather experiences, at successive ages, during 1935 had both the lowest proportion than material or maternal opportunities, their reproductive lives. childless and the highest TFR. The the degree of kin availability—that is the Within this report, the experiences fertility of women who were born in presence of children and the children’s of three cohorts of women are followed 1960 is characterized as intermediate to spouses—is of great importance for the over consecutive years through their the other cohorts in terms of elderly. Consequently, the proportion of respective reproductive lives. In childlessness, but is distinct with both women with any offspring is key to contrast, analysis of period data includes lowest levels of childbearing and oldest the well-being of families in these the observation of many cohorts within ages of first births. First-time societies (2). a given time interval (1 year, for childbearing is more concentrated (that is, least spread out) by age of mother Childlessness has increasingly example), with mixed and different for the 1910 and 1935 cohorts than the become an acceptable lifestyle in North experiences of their reproductive lives. 1960 cohort. Finally, data for all U.S. America and Europe. However, lifestyle The data for this report come from birth cohorts 1910–1960 suggest that decisions are only one of the reasons for publications based on U.S. vital the greater the proportion childless in a having a child. Not having a child may statistics data: ‘‘Fertility Tables for Birth cohort, the lower the TFR. be due to postponement of childbearing, Cohorts by Color: United States, rather than early sterility (such as 1917–1973’’ (4), Centers for Disease • Keywords: birth cohorts cohort premature menopause). Intervening Control and Prevention’s National • • fertility life table methods zero parity factors leading to childlessness include Center for Health Statistics (NCHS)

Page 1 Page 2 [ Series 2, No. 153 tables from the vital statistics of the classification) of live birth order and age and to estimate other duration functions. United States (5,6), and the recent of mother also improved, with relatively Its applications are common in survival NCHS Internet release, ‘‘Cohort Fertility few births imputed for live birth order analysis, medical trials, and a number of Tables for All, White, and Black and age of mother not stated. For a reproductive health topics. The life Women: United States, 1960–2005’’ (7). detailed discussion on the adjustment of table—or in this case, the ‘‘maternity The selection of these three birth births and imputation of missing data, table’’—functions were calculated in a cohorts was based on several criteria. see references 4 and 7. spreadsheet format using Excel, wherein The cohorts chosen experienced their the calculations from one table column prime childbearing years under differing Analytic Methods become the basis for the next. The social, economic, and demographic following describes the most basic conditions, and were evenly spaced from The life table method is most functions. each other. The birth cohorts selected commonly applied to mortality data to Size of maternity table’s initial were 1910, 1935, and 1960, which are analyze the probability of dying in a cohort, or ‘‘radix’’—For purposes of spaced 25 years apart. This spacing is particular time period such as 1 year comparison, each cohort in the maternity close to the mean length of a generation, and to estimate a variety of statistics table is standardized to 100,000 at age which empirically has a mode of 27–28 such as the average expectation of life 15 (expressed as l15 in formal terms). years (8). Moreover, these cohorts had at birth. However, life tables can also be Probability of having a first birth at data for essentially their complete used to study how long it takes for any age x (the qx values)—Represent the reproductive lives; that is, ages 15–49. event to happen. Some examples of probability or chance that a woman who Note that the data for the 1960 cohort reproductive health applications include: is childless on her xth birthday will have are only available through age 45. estimating the average time to a child before reaching her xth+1 However, this was deemed acceptable conceive (10), gauging pregnancy birthday. because the cohort had essentially outcomes (11), measuring the mean Number of first births occurring at completed its childbearing. duration of breastfeeding (12), age x (the bx values)—Represent the In essence, the data represent three evaluating contraceptive use number of first births who are born to a generations of women who experienced duration (13), cumulating birth woman at age x. markedly different conditions. The probabilities within first marriages (14), Number of childless women at age x earliest cohort of women spent their and measuring the duration of (the lx values)—Represent the number of prime childbearing years (ages 20–35) cohabitation, marriage, divorce, and women who are still childless on their during the Great Depression (1929 to remarriage (15). This is the first time, xth birthday. the start of World War II), the second the authors believe, that life tables have Cumulative probability of having a during the post-World War II economic been used to formally examine and first birth by age x—Derived by recovery and the ‘‘Baby Boom’’ years compare patterns of childlessness. The subtracting the lx value from the radix (1946–1964), and the third during a tabular data (4–7) produce functions that and dividing that difference by the radix period of social and economic relate to both childlessness and first to obtain a cumulative indicator of the liberalization (which began in the late birth; as such, the tables are referred to probability of first births in a cohort. 1960s) with relatively low and definitely in this report as ‘‘maternity tables.’’ Number of years expected to remain delayed fertility (1973–2005). Several maternity table functions childless from a given age to age 50

Data for the 1910 and 1935 that are used in the analysis are briefly (the ex values)—Represent the average cohorts were taken from earlier discussed in the next section. The time remaining in a woman’s sources (4–6) and data for the 1960 complete maternity tables are included reproductive life that she would expect cohort were from the most recent as Tables 1–3. Unlike standard life to be childless. It has a well-known source (7). tables, which range from birth to the counterpart in life tables: the expectation oldest measureable age, the maternity of life. Data Quality table starts at age 15 and ends at age 49. A more detailed description of the These ages typically represent the functions is provided in the ‘‘Technical Note that the data in this report beginning and end points of the Notes.’’ Two other related functions are encompass a period where birth reproductive period. As seen in described below. registration completeness improved to Tables 1–3, less than 1 percent of first Indicators of dispersion (Gini become effectively universal. Three births occur after age 45 (i.e., column Concentration Ratio and Duncan Index nationwide tests of birth registration bx, births). of Concentration)—Represent two completeness estimated that of all births measures of spread (or dispersion) in occurring in the United States, Measures volume and timing of childbearing. Both 92.5 percent in 1940, 97.9 percent in depend on the Lorenz curve of 1950, and 99.2 percent in 1964–1968 As noted earlier, the life table cumulative dependent variables. While were registered (9). Accordingly, births method is most commonly applied to most known for indicating economic for earlier data years were adjusted for mortality data to analyze the probability and geographic inequality, they have underregistration. The quality (as well as of dying within a given time interval also been used to reflect maternal and Series 2, No. 153 [ Page 3 child health inequality (16,17). Both measures indicate the concentrations of 1910 cohort 1935 cohort 1960 cohort first births by age of mother. The differences in the two indices are 0.160 discussed below. 0.140 Lifetime total fertility rate by birth cohort (TFR)—The age-cohort-specific 0.120 central fertility rates (fx) are summed over a cohort’s 35-year reproductive 0.100 period to provide the completed fertility rate for that birth cohort, expressed as 0.080 number of births per 1,000 women 0.060 (aged 15–50). Probability of first birth 0.040

Results and Discussion 0.020

0.000 The birth cohort of 1910 turned 25 15 20 25 30 35 40 45 49 in 1935, during the Great Depression. At Age in years that time, many marriages were delayed due to the lack of employment SOURCE: CDC/NCHS, National Vital Statistics System. opportunities for men. The average age Figure 1. Probability of having a first birth, by age and birth cohort of mother: of marriage increased and a record United States, 1910, 1935, and 1960 number of women never married (18). Women at age 25 remained childless for improvements in opportunities for of childless women born in 1910 had a more years than did those in the other women. Also at this time, there were first birth at age 23. The greatest cohorts during comparatively better changes in the service sector in the U.S. number of first births occurred early in economic times; they expected 14 years economy (especially for professional, the reproductive period. The of future childlessness compared with 11 managerial, sales, and technical probabilities for first births dropped years for women born in 1935 and services) (20), which favored the rapidly after age 25. This is not 1960. employment of women. Just as unexpected given that the United States The birth cohort of 1935 turned 25 importantly during this time, modern was deep into the Great Depression at in 1960, at the height of the prosperity methods of contraception became widely this time. that contributed in part to the Baby available (21,22). The birth cohort of 1935 entered Boom. At this post-World War II time, prime childbearing years during the the economy had grown rapidly and Patterns of First-birth economic prosperity of the late 1950s headed to full employment and high and early 1960s. This cohort had the wages. Men with only a high school Probabilities (qx) highest overall fertility and lowest level education could earn enough money to During each year of a childless of childlessness. The highest first-birth support a family (19). Prior to World woman’s reproductive life, there is some probability occurred at age 24 when War II, few attained higher levels of probability that she will give birth. If about 15 percent of women still education. Post-World War II, the G.I. she does not, she remains childless and childless had their first child (Table 2). Bill assisted veterans in both obtaining has the opportunity in the succeeding The probability curve was similar to that higher education and supporting a year to have a birth. The shapes of of the 1910 cohort, but first-birth family. At the same time, women were first-birth probabilities differ greatly probabilities were higher than those of staying at home, having at least two among the three cohorts. They are the 1910 cohort until age 39. children. This was due both to distinguished by overall magnitude of The initial slope of first-birth their husbands functioning as the sole the first-birth curve, its symmetry, and probabilities for the 1960 cohort (to provider in the household and to social the peak age to give birth (Figure 1). age 20) was not as steep as those of and workplace discrimination, which Of the three cohorts, the 1910 the previous cohorts. After age 20, the curtailed the employment of married cohort’s attainment of motherhood was probabilities remained fairly constant women and, particularly, mothers (19). the lowest. The greatest probability or for 10 years. The cohort’s highest The birth cohort of 1960 turned 25 likelihood to have a first birth at a given probability of having a first child in 1985, during a period of increasing age was 114 births per 1,000 (or 6,126 occurred comparatively late, at age 29, educational attainment and sustained of 53,737 childless women). This peak with the chance that 1 out of 10 labor force participation for women. of first births occurred at age 23 childless women would have their There were legally enforced (Table 1). Put another way, 11.4 percent first child (Table 3). Overall, the Page 4 [ Series 2, No. 153

Table A. Cumulative probability of first birth, by selected age and birth cohort of women: proportions childless found in the United States, 1910, 1935, and 1960 National Fertility Survey (23) and the Birth cohort National Surveys of Family Growth (3). In the last 10 years of their Age of women in years 1910 1935 1960 reproductive periods, the proportions Cumulative probability of first birth childless in the three cohorts were 18...... 0.087 0.108 0.093 approximately equally spaced (Figure 3). 22...... 0.397 0.457 0.329 This was not true at earlier ages. Due to 25...... 0.576 0.663 0.482 the postponement of first births by the 30...... 0.723 0.825 0.686 35...... 0.778 0.869 0.794 women in the 1960 cohort, a relatively 49...... 0.803 0.886 0.844 large number of the 1960 cohort were childless at younger ages. It was not until women in the 1960 cohort were aged 33 that they crossed under the 1910 cohort 1935 cohort 1960 cohort ‘‘survival curve’’ of the women in the 1.000 1910 cohort. From that age forward, a 0.900 relatively larger proportion of the 1910 cohort than the 1960 cohort was 0.800 childless at each age (Figure 3 and 0.700 Table B).

0.600 Distribution of First Births 0.500 by Mother’s Age (bx) 0.400 As shown in Table B, a substantial 0.300 number of women did not have children 0.200 by the time they concluded their Cumulative probability of first birth 0.100 reproductive years. However, approxi mately 80 percent to 90 percent of the 0.000 women in all three cohorts did have at 15 20 25 30 35 40 45 49 least one birth. The distributions of first Age in years births vary by peak, shape, and overall SOURCE: CDC/NCHS, National Vital Statistics System. magnitude of first births for these three Figure 2. Cumulative probability of having a first birth, by age and birth cohort of mother: cohorts of 100,000 women. These United States, 1910, 1935, and 1960 differences are shown in Figure 4 and Table C. first-birth probability curve for the Number in Cohort The fewest first births were born to women in the 1910 cohort. For each 1960 cohort shifted considerably to Remaining Childless, by the older ages relative to those of the 100,000 women who entered their earlier cohorts. Age (lx) reproductive period in 1925, 80,300 Table A compares the cumulative became mothers between ages 15 and Because the size of the initial first-birth probabilities at important ages. 49 (Table A). It was at age 19 that the cohort is set at 100,000, the number of Among them are: age 18, when high greatest numbers of births occurred; that women in column l (Tables 1–3)atage school is generally completed; age 22, x is, 81 births per 1,000 women (or 8,100 49 represents the number out of the when college is completed; and age 35, per the original 100,000 women born in original 100,000 who remain childless at when motherhood has essentially been 1910). Of the 1910 cohort, one-half of that age. initiated. For these three ages, the 1935 the first births were born to women As illustrated in the inset of cumulative birth probabilities were the before age 21.1 and the other one-half at Figure 3, about 19,700 out of the highest (0.108 at age 18 and 0.869 at later years (Tables A and C). 100,000 women of the 1910 cohort age 35). The 1960 cohort’s cumulative Many more first births occurred to remained childless at the end of their probability was relatively high at age 18 women in the 1935 cohort than in the reproductive period. That is, 0.197 of (0.093), but quickly dropped below 1910 cohort: approximately 88,600 of that cohort were still childless at age 49. those of other cohorts at age 25. the 100,000 women in the 1935 cohort For the 1935 cohort, the relative However, at age 35, women born in within their 35-year reproductive period. proportion was 0.114, and for the most 1960 had a higher probability of having This level is 10 percent higher than that recent cohort, 1960, it was 0.156. These had a first birth than the 1910 cohort of the 1910 birth cohort. It was at age figures correspond well with the (Figure 2). Series 2, No. 153 [ Page 5

20, the peak age for first births, when 1910 cohort 1935 cohort 1960 cohort 92 births per 1,000 took place for women born in 1935. One-half were 100,000 born before age 20.8 for the 1935 cohort 90,000 and the other one-half at later years 80,000 (Tables A and C). The number of first births born to 70,000 women in the 1960 cohort was 60,000 intermediate to those in the 1910 and 1935 cohorts (roughly 84,400 women 50,000 had a first birth compared with 80,300 40,000 and 88,600). But the volume of first Number of women births is not the only distinguishing 30,000 characteristic of this cohort. The peak of 20,000 the distribution is 63 births per 1,000, a 10,000 peak that is about two-thirds the number of births that occurred in the 1935 0 cohort table (also at age 20). The shape 15 20 25 30 35 40 45 49 of this distribution is markedly different Age in years as well: the decline in numbers of first NOTE: Based on initial cohort of 100,000 women aged 15. SOURCE: CDC/NCHS, National Vital Statistics System. births is particularly more attenuated than it was for the earlier cohorts. This Figure 3. Number of women remaining childless, by age and birth cohort of mother: United moderate level extends into older years. States, 1910, 1935, and 1960 The midpoint is about 2 years older for the 1960 cohort than that of the 1935 Table B. Proportion of women childless, by selected age and birth cohort of women: cohort (Table C). United States, 1910, 1935, and 1960

Birth cohort Expectation of Number of Age of women in years 1910 1935 1960 Years to be Childless in the l /100,000 Future (e ) x x 18...... 0.913 0.892 0.907 A woman may give birth in the first 22...... 0.606 0.543 0.671 25...... 0.424 0.337 0.518 12 months of her reproductive life—that 30...... 0.277 0.175 0.314 is, at age 15—or she may have her first 35...... 0.222 0.131 0.206 birth at the end of the maternity table 49...... 0.197 0.114 0.156 when she is in her 40s. However, it is most likely that she will have her first birth, if she does become a mother, in her 20s. It is not only of interest age (qx) and the number of women who childlessness compared with the 1910 whether a woman will or will not remain childless at that age (lx). The cohort, although the shapes of the become a mother: a discrete outcome. It expected childless years begin to decline curves were similar (Figure 5). is additionally of interest to know the sharply when the number of childless At age 15, women of the 1910 average number of years that she women remains fairly constant: around cohort anticipated being childless for an remains childless during the period age 35 for each of the three cohorts average of 13.4 years; those of the 1935 when she could potentially have a child. (Figure 3). Thereafter, with each year of cohort, 10.8 years. After age 30, the two This is an important statistic because it life, the expected number of childless curves followed similar patterns. speaks to the opportunity costs a woman years decreased annually by The childless-years curve remained may have in completing her education approximately 1 year (Figure 5). rather flat for the 1960 cohort as the and job training during years when her The 1910 cohort had the highest first-birth probability curve was quite childbearing potential is comparatively overall level of childlessness and thus wide (as in Figure 1). As seen earlier in high. the average number of years expected to Figure 3, the number of women The average number of years a be childless followed the highest curve remaining childless stayed fairly childless woman at a given age is of the three cohorts. It reached a high of constant up to age 35. This is when the expected to remain childless is shown in 15.4 years at age 30 (Table D). average expected number of childless Figure 5. This measure is a function of For ages 15–30, the 1935 cohort years dropped constantly with each both the birth probabilities at a given had substantially lower levels of increasing year of age (Figure 5). Page 6 [ Series 2, No. 153

number of first births in the maternity 1910 cohort 1935 cohort 1960 cohort tables is different for each cohort (80.3, 10,000 88.6, and 84.4 thousand first births). 9,000 To easily compare the information of concentration (or inequality) shown 8,000 in the Lorenz curves, the Gini ratio can 7,000 be used. It is the index associated with the proximity of the Lorenz curve to the 6,000 diagonal line of equality. The Gini 5,000 concentration quotient is the ratio of the 4,000 area that lies between the Lorenz curve and the line of equality to the total area Number of first births 3,000 below the line of equality (24). The ratio 2,000 range is 0–1. The higher the coefficient, the greater is the concentration or 1,000 inequality. Table E shows the ratios for 0 the cohorts of 1910 and 1935 to be 15 20 25 30 35 40 45 49 similar (0.534 and 0.563, respectively), Age in years but the ratio for 1960 is notably lower NOTE: Based on initial cohort of 100,000 women aged 15. at 0.447. This lower figure illustrates the SOURCE: CDC/NCHS, National Vital Statistics System. greater dispersion in age of first births Figure 4. Distribution of first births, by age and birth cohort of mother: United States, 1910, for the most recent cohort. 1935, and 1960 As stated earlier, indicators from the Lorenz curves provide concrete Table C. Mean, median, modal, and maximum number of first births (bx), by birth cohort of information about the pacing of first women: United States, 1910, 1935, and 1960 births. At 50 percent of cumulative years Birth cohort exposed (to age 32.5), the cumulative proportions of first births were fairly Summary indicators of first birth, by cohort 1910 1935 1960 similar (in 1910, 95 percent of first Meant age a firstbirth ...... 22.7 22.1 24.2 births; in 1935, 97 percent; and in 1960, Medianage a tfirst birth ...... 21.1 20.8 22.7 90 percent). But at a cumulative Modal (most common) age at first birth ...... 19.0 20.0 20.0 25 percent of years exposed (to age 23), Maximum number of first births (bx)at any age ...... 8,102.0 9,241.0 6,289.0 the differences in cumulative proportions of first births are markedly different (in 1910, 65 percent; in 1935, 68 percent; and in 1960, 52 percent). years exposed to childbearing. The Degree of Concentration of This is another way of expressing the points on the Lorenz curve represent First Births lower concentration of first births for statements like ‘‘in the first 35 percent the 1960 cohort (Figure 6). Another way to view the of 1935 cohort’s reproductive years (that A second indicator of concentration, distribution of first births relative is, by age 27.25), 90 percent of the first the Duncan index, is also shown in to age of women is in terms of births were produced.’’ A 45-degree Figure 6 (25). Geometrically, this index concentration (2). Concentration analysis diagonal line that runs from 0 through is the maximum vertical distance from generally studies the degree to which a 100 percent shows the condition of the diagonal line to the curve, showing certain proportion of producers (in this equal distribution, where the probability the exact point where there are the case, women of fertile ages) dominate a distribution of having a first birth holds greatest deviations between the diagonal market (here, first-born children). The constant across ages. That is, by age line and the Lorenz curve. It is greater the degree of concentration (as 32.5 (the midpoint between ages 15 and calculated by subtracting at each age the measured by the Gini or Duncan 50), 50 percent of women would have value of the diagonal from the value of indices, for example), the greater is the had their first birth. the Lorenz curve. The greatest concentration of first births among Several Lorenz curves can be difference indicates the age where the women in particular age groups. mapped on the same graph regardless of concentration is highest. Lorenz curves provide a visually the total number of events occurring as As illustrated by the lengths of interpretable basis for comparing these the Lorenz curve and its related these vertical lines in Table E,the two indicators of concentration. The indicators are independent of scale. cohorts of 1910 and 1935 have the Lorenz curves in Figure 6 map the Accordingly, Figure 6 plots first-birth greater indices of concentration (0.491 cumulative proportion of first births of a concentrations for each of the fertility and 0.523), and the 1960 cohort index cohort to the cumulative proportion of cohorts even though the cumulative age Duncan additionally, concentration greatest, 31 sum, is but highest or cumulative of women: has vertical Table the woman mother: based values has Figure 30–50 15–50 SOURCE: CDC/NCHS,NationalVital StatisticsSystem. NOTE: Referstonumberofyearswomenmayexpectremainchildlessfromcurrentageendreproductiveperiod. higher, 27 1.0; that Gini the a the (age

The Number of years the D...... value years. on 10.0 12.0 14.0 16.0 18.0 5. may the the vertical 0.0 4.0 6.0 8.0 2.0 concentration lesser United is United difference Expected index Average calculations. with Duncan 31). 1935 the at g nevlo oe nyears in women of interval Age exposed horizontal vertical age of be 0.542. For the same 5 0 5 0 5 0 5 49 45 40 35 30 25 20 15 and a value occurring States, States, 0.506 cohort compared measure proportion distance 1960 1935, number calculations number the for number to In distance (0.401). out 1910, 1910, position is childbearing. The has 1960 1960, cohort the the also

at of of of of of as the 1910 greatest point of 1935, 1935, the years of concentration 0.422. years the a is they it These at has 37 percent highest reinforce maximum years is is the oldest lowest; age cohort and of and at expected at are a childless,

In the age 27, a 1960 1960 1910 cohort Age inyears to by

remain through (1910, proportion pattern One trends concentrated (whether concern. period TFR produce distribution parities. two, course, cohort’s in Importance of selected the the Childlessness interesting 1910 three, 15.4 13.4 at childless, in is 1915, of those the 1960.

It cohorts’ fertility The age Demographic 20th five predominately not the is childless four, end of 1935 cohort interval or the 1920, the timing women decades TFR these by illustration of dispersed) Century it cohort Birth and behavior. totality only TFRs. of is the age 1935 14.3 10.8 with etc.), e for and parities of but x even Childlessness who indicator of reproductive

and childbearing the Moreover, early respect birth one of from childbearing. higher There have marks birth of the cohorts that aspect Context 1960 cohort cohort or this 1910 of cohort had to late, 1960 are, 12.0 13.6 broad is the the of one, of the of of a Figure 8. these percent fertility had zero, (35 percent) of characterized began corresponding sustained 1900–1960. childlessness highest been more childless of 1935 childlessness in component noted, stayed cohort’s children. points cohorts 1950–2005. interest, provides women was of of of (Figure 8). childbearing. (Figure 7) completed frequencies women years Distribution Trends Cohort 20th 1910–1915. women the their the children historically Figures 7 The due seen one, cohort three children after before historically 1910 in childlessness historically Century levels distribution were who have of reproductive the TFR to cohort the and In the a and in and with four parity The the by cohorts TFRs, of the born TFR of fact, cohort The TFRs During and was TFRs had the curve essentially of of located TFR 1995 parity-one by was of and the (37 percent), TFRs. three. eo and zero- the birth The higher eis2 o 153 No. 2, Series low or two Parity TFR low 1935 1910 to cohort moderate close distinctively birth women due the zero, for TFR; lowest of near more 8 three high is in for (Figure 9). shown is and women high for this completed is children of levels show proportion The all years. is the near the 1950–2005 to clearly influence and cohorts proportion an to the one, the the a the measured the for of the a cohorts cohorts period children. women completed TFR higher-order average with 1910 2.0. high levels 1960 important combination 1960 two in years relative 1960 parities of cohort parity 1935 women by Figure 9 than or high Figure 9 shown completed high This of four of It point. two low the and fertility cohort of the and of childless [ and the was had number of The 50 for when end ae7 Page of levels level or 1960 their born low in the As 1950. cohort members employees further were, fathers that rates. terms years War second-, women: women marriage Depression economic from in considerations, Great few Table United in Gini ucnIndex Duncan reproductive Figure Page SOURCE: CDC/NCHS,NationalVital StatisticsSystem. NOTE: Vertical linesrepresentDuncanIndexofConcentration. marriages, 1910 ocnrto Ratio Concentration In In the years Cumulative proportion of first births II 8 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 that E. both Some in of Depression. World 6. States, started contrast, general affected [ suppressed being would United Gini children began the Lorenz or large lowered of Series of circumstances before in fConcentration of of .0 .0 .0 .0 0.80 0.60 0.40 0.20 0.00 coupled higher-order demographers Concentration the end, 1929 (26). War Measures experience away down 1910, terms war-related their numbers States, normally in terms, there the curves 2, Armed the who the never 1925, II the No. Due completed ...... 1935, reproductive from mid-childbearing 20 percent of women had with of was beginning 1910, probabilities 153 were the of uncertainty dispersion to The born (18). Forces of a have of ended; birth. and of ...... home, first the

a lifetime industries time economic Ratio potential concluded 1935, women postponed sudden the of difficult 1960 Cumulative proportionofyearsexposed decline births fertility a World the in only and Great first-, of and the which ages and 1932 and the 1935 that born drop and Duncan had a 1960 in in in Duncan 1910 cohort Index reflected fertility birth have 1935 addition, support, postpone those distributions parenthood. early The Veterans and growth 1946) (26). aided increase number prospered (19). married returned Index of its For As There prosperity 0. 0.534 1910 (Figure 7)(7). a cohort of and by 491 Concentration, second-, supplements in shown of fell of the life, a it in

almost home to in the family

nearly the variety Concentration, was was marriages, 1 In live pre-World the who after were With 1935 cohort and G.I. year economy, addition above, to that a not third-, 1960 all singly Birth formation. universal had dramatic the 1980, markedly Bill. start such of alone 0. 0. of 1935 necessary it 563 523 were cohort reasons, children by economy cohort’s completed the ensured or with War This or

or means to which

birth families (1945– higher-order

by women to married (27). sufficient the marriage jump II different a birth legislation resume cohort period. 42-percent 1960 cohort went cohort to rapid of fertility led was parity in cohort: in 0. 0. were 1960 to 447 401 on the the of from for and 1.00 In to

motherhood women found attainment (32). childless childless (31). also labor numbers control (21,22), of women (7), of included delayed characteristics. detailed section that for of started the prior children shows Northern ‘‘postponed’’ and decline of reaches actually proportion young in magnitude ‘‘recuperation’’ terms recuperation trends Recuperation Postponement Postponement only Childbearing postponement childbearing. ability one-half low-fertility the coitus-independent completed the actual the life it Postponement Cohort An number became when to force (30). ‘‘postponement’’ that is form United of that women, to among 1940 2.6 of in with the essential their marriage (29), discussion postponed borne clear of of delaying diverged postponement and postponement study the these they of and the the in a end fertility women the of with countries had more in initial birth 27th births postponement The century parity Western the States, Frejka number how of It the a respective by average Some timing which are timing widespread major could and of More women. fertility Less has halved childbearing. aspect a fewer last American first cohort cohorts by birthday likely of its becomes of many dual professional desires were who analysis for the of been and Canada, of and has childbearing educational combine educated means childbearing is this during timing century educated of of Europe. of a births (28), and number black as births and substantial of for measures these a Fertility decline entered major For to born births. fertility. at Sardon of generation births. been observed of combination issue, well trends to had availability stay the takes 1.927. then the women apparent provides of a the the trends remain and reasons were showed later Table F more decline women 1980 of as women peaked fertility life. What The among see the 1940s past (33). place in of a But age in that in the Corresponding Annual Cumulated Corresponding Annual time the Cumulated considerable phenomenon been terms. States ages cohorts Table F cohort phenomenon . Table Recuperation childbearing birth Figure Data - - - SOURCE: . SOURCE: CDC/NCHS,NationalVital StatisticsSystem. . Category Total

window Proportion per 1,000 women Childbearing 100 200 300 400 periods of paid cohort F. rates rates not 7. in Recuperation SOURCE:

rates , 0 fertility Total 27 of

had age-specific age-specific Parity not available. both of of in the 1900 and Postponement applicable.

span span change change in in (i.e., slowed fertility rates, delay, in the data. although of Frejka relative 1970s distribution Table F the

over. the of of increase literature from through

by recuperation birth birth T, of of cohort cohort Due Parity 0 later

again overview

Sardon rates, age percent percent down

Less in

27th cohorts cohorts , and there 1910 up to group there rates rates the childbearing JP. in to to shown by age the at ...... attention to

among absolute Contemporary 40th age

United age-specific are and completed ...... selected this are of length

26). 26 is birthday birth Parity 1 in fewer the birth 1920 The has cohort childbearing of age fertility group Birth cohort trends Parity 2 change been older robust 1960 cohorts in recuperation for cohort childlessness distributions Childlessness Relationship 1930 of and Table F in birth ages 1930 As low-fertility 1.389 1.795 positive: birth ages birth - –4.923 -- - 0.710 -- recuperation . . fertility in . . seen dropped cohorts: 27–40 . . ,

the such cohort, the cohorts countries: 1940 Parity 3 or of earlier, affect preceding 2 percent. cumulative rate, 1930–1940 1930–1940 for ‘‘catching births that below United 0. 1. 1940 A there of 849 927 the of long-term the of but to trends the women: for

fertility

1930 States, one. completed

trends 1950 TFRs had annual decade other Parity 4ormore perspective. up.’’ fertility in For been birth United 1900–1960 1940–1950 1940–1950 in in As parities rates –0 –5 had the 0. 1. 1950 the the .178 .032 Marrakech, a 834 165 rates seen 1960 States, of

Birth Morocco: 1930, cohort Figure 10, regression of a between the fertility and relationship was 2005. of States) were than report various childless cross-sectional TFR. the completed authors (35,36), childless childless elevated point cohorts second for trends segments affect well. Figure 7) between produce y 1950–1960 1950–1960 –1 7.5-percent axis XXVI 0. 1. 0. 1960 childless completed .577 1940, the TFR percentage 988 694 995 the As The a those from Taken of However, IUSSP the general (Figure 10) in (Figure 10). and 1910–1935

is seen points. (the TFR. was inflection). a proportion percentage childlessness observation declined 1950, from has contributes Figure 9), and produced for completed shift International was a of fertility one represent women. between together, calendar negative also in been the increase fertility other When completed but 1960, numerous childless, TFRs The 1960–1970 1960–1970 applied country in other Series these showing –0 measured. 1935–1960 0. 1970 by -- -- loose the

are .172 mapped Population 978 (34). The birth analysts: with in data childless 1970, of least to fertility has proportion one and a publications, these year relationship from 2, examples relationship less the ( in

women to continuous y (the low first No. negative The cohorts shown two the fertility the been countries that axis

and child proportions squares Conference. the observed 1980 ambiguous by factors 1950 153 levels Namely, United segment lower the proportion proportion rate birth and major 1980 the data in 1970–1980 1970–1980 other that who for –0 in used [ childless is 0. and data 1980 through (TFR, -- -- .312 higher as 948 2009. of this in Page the there series at an the are the is

9 Page 10 [ Series 2, No. 153

1956 cohort (1.99) with the proportion 1910 cohort 1935 cohort 1960 cohort childless at 16 percent. The horizontal 40 ranges in TFRs are similar; however, the magnitudes of the slopes describing the 35 trends between the cohorts of 1910 and 1935, and 1935 and 1960, are 30 substantially different. The relationship 25 between the TFR and percentage childless is much stronger between the 20 1910 and 1935 cohorts (slope equals

Percent 13 percent) than it is between the 1935 15 and 1960 cohorts (slope equals 6 percent). Only one-half the change in 10 percentage childless was needed in 5 recent years to produce the same amount of change in the TFR as in 0 earlier years. In other words, the TFR 0 1 2 3 4 or more would increase by one child when the Number of children proportion childless decreases by

SOURCE: CDC/NCHS, National Vital Statistics System. 13 percent in the 1910–1935 cohort segment, and for the 1935–1960 cohort Figure 8. Percent distribution of the number of children ever born, by birth cohort of segment, the TFR would increase by mother: United States, 1910, 1935, and 1960 one child when the proportion childless decreases by 6 percent. A demographic explanation may be 3,500 given for these differential slopes. As can be seen in Figures 7 and 8, between the 1910 and 1935 cohorts, the 3,000 proportion childless dropped greatly as the proportion of women of high parity rose to historically high levels. 2,500 While the 1960 cohort had lower completed fertility than did the 1910 2,000 cohort, the percentage childless was lower. The differences in final levels 1910 cohort 1935 cohort 1960 cohort Rate per 1,000 women (estimated) were greatly affected by achieved 1,500 parities of four or more, so that the overall fertility of women in these earlier cohorts with their greater family 0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 size was less affected by the proportion Year cohort completed fertility of childless women than the later cohorts with their smaller family size. NOTE: Based on total fertility rates for women aged 45–49. SOURCE: CDC/NCHS, National Vital Statistics System. Hence, in these series, the TFR depends not only on the percentage childlessness, Figure 9. Total fertility rates at completed fertility of birth cohorts: United States, 1950–2005 but on the entire fertility distribution. There is little variation in data However, given the presence of a Starting with the cohort of 1910 for points around the long-term trends continuous series of data points, the which the TFR was 2.3 and more than represented by the long segments in outcomes are even more informative. 20 percent of the cohort was childless at Figure 10. The amount of variation Figure 10 depicts an annual plotting of age 50, each successive cohort through explained by the least squares equations the proportion of 1,000 women at age the cohort of 1935 had a higher TFR linking childlessness and completed 50 who are childless, by the and lower percentage childless. The cohort fertility is quite high: 82 percent corresponding TFRs. Each point in cohort of 1935 had a TFR of 3.2 with for the more recent segment of years Figure 10 represents a birth cohort that less than 10 percent of the cohort and 92 percent for the previous ones. can also be defined as the year that remaining childless. Cohorts after 1935 These tight relationships imply strict cohort reaches age 50. The figure shows had decreasing TFRs and increasing trends in U.S. demographic history that how the TFR and the percentage percentages childless with the lowest were reversed when a series of events childless changes over time. completed cohort TFR occurring in the related to post-World War II prosperity Series 2, No. 153 [ Page 11

women married young, began their 250 childbearing young, and were the cohort 1910 (1955) among the three to have the least 200 childlessness. 1960 (2005) The 1960 birth cohort moved 1955 1915 1920 150 through a very different socioeconomic 1925 era. The obstacles to educational and 1930 1935 1950 (1980) employment opportunities were 100 eliminated. Along with the availability 1945 1940 of modern contraception, ‘‘choice’’ in 50 whether and when to become mothers is shown by the first-birth probability curve. Proportion childless per 1,000 women This concentration curve is far flatter than 0 2,000 2,200 2,400 2,600 2,800 3,000 3,200 that of the other two cohorts. The Rate per 1,000 women proportion of women who had first births is intermediate and the concentration NOTES: Year cohort completed fertility in parentheses. Based on proportion childless and total fertility rate for women aged 45–49. SOURCES: CDC/NCHS, National Vital Statistics System and Table 186 of reference 7. measures of first births are the lowest. The TFR of the 1960 cohort (2.00) is among Figure 10. Proportion childless and total fertility rate at completed fertility, by birth cohorts: United States, 1910–1960 the century’s lowest. What will the future hold for the next generation, the birth cohort of reversed the decline in fertility that had having completed four or more years of 1985? It began its childbearing years in been occurring for decades. college had more than tripled (38). a society socially divided on means and An economic interpretation for the Studies (1,3) found that older women financing of fertility regulation. childlessness–TFR relationship has been are childless for both voluntary and Childbearing outside of marriage has noted. Once a family has a child, it may involuntary reasons; age is the primary increased significantly (40): the go on to have more children because explanatory variable for involuntary percentage of births occurring outside of any goods are substitutable. For childlessness for older women due to marriage has increased from example, goods can be passed on from subfecundability and decreased partner 33.2 percent in 2000 when the cohort one child to the next, a car can hold availability. In the United States, was aged 15, to 41 percent in 2009. The three children as well as it can hold one, childlessness may have plateaued (3) or cohort moved into its key childbearing two children may share a house as may continue to rise as this country years during a significant recession; easily as may one, etc. (2). It has been adopts more of the demographic and fertility dropped in 2009 to replacement further observed that in recent times, social attributes recently seen in levels (40). A repeat of the current study once having had one child, the Europe (39). could be made in 10 years, using similar probabilities to have additional ones In sum, the various indicators for measures, providing better insight on the have remained fairly high (1). the transitions to first birth for the 1910, socioeconomic factors affecting the 1935, and 1960 birth cohorts are closely first-birth transitions of the 1985 cohort. tied to the social, economic, and Conclusion historical features of the periods during which these women spent their References Current low and late fertility and childbearing years. The 1910 cohort increased childlessness has been passed the important portion of its 1. Testa MR, Toulemon L. Family observed in all of Europe and in much childbearing years during the Great formulation in France: Individual of North America. This ‘‘second Depression. Average age of marriage increased while a record number of preferences and subsequent outcomes. demographic transition’’ (37) is Vienna Yearb Popul Res 41–75. 2006. women never married. Of the three consistent with an observed increase in 2. Lutz W. Comparative analysis of cohorts, the 1910 cohort had the largest individual autonomy and a growth in completed parity distributions: A global proportion of women who did not have gender equality. At the same time, there WFS perspective. Popul Bull UN is the increase in socioeconomic children. As well, the largest proportion 28:25–57. 1989. activities competitive with childbearing. of these women had only one birth, 3. Abma JC, Martinez GM. Childlessness In the United States, education and contributing to the low TFR of 2.35. among older women in the United career have been reported as important The 1935 cohort passed its principal States: Trends and profiles. J Marriage factors in women’s decisions to delay reproductive years during the prosperous Fam 68(4):1045–56. 2006. 4. Heuser RL. Fertility tables for birth marriage and motherhood. From 1970 to post-World War II era. Men were often cohorts by color: United States, 2005, the female labor force sole bread earners and many factors kept women in the home with their roles 1917–1973. DHEW Publication No. participation rate increased by 76–1152. Rockville, MD: National circumscribed to motherhood. These 37 percent and the percentage of women Center for Health Statistics. 1976. Page 12 [ Series 2, No. 153

5. National Center for Health Statistics. 19. Casper LM, Bianchi SM. Continuity 33. Frejka T, Sardon JP. The postponement Vital statistics of the United States, and change in the American family. of childbearing. In: Childbearing trends 1974. Volume 1, Natality. 1978. Thousand Oaks, CA: Sage Publications, and prospects in low-fertility countries: 6. National Center for Health Statistics. Inc. 2001. A cohort analysis. Dordrecht, NL: Vital statistics of the United States, 20. Wyatt ID, Hecker DE. Occupational Kluwer Academic Publishers. 2004. 1999. Volume 1, Natality. 2001. changes during the 20th century. Mon 34. Feeny G, Lutz W. Distribution analysis 7. Hamilton BE, Cosgrove CM. Cohort Labor Rev 129(3):35–57. 2006. of period fertility. In: Lutz W (ed.). fertility tables for all, white, and black 21. Mosher WD, Westoff CF. Trends in Future demographic trends in Europe women: United States, 1960–2005. contraceptive practice: United States, and North America: What can we Internet tables. Hyattsville, MD: 1965–76. National Center for Health assume today? London, UK: Academic National Center for Health Statistics. Statistics. Vital Health Stat 23(10). Press. 1991. 2010. Available from: 1982. 35. Barkalov NB. The fertility decline in http://www.cdc.gov/nchs/nvss/ 22. Abma JC, Chandra A, Mosher WD, et Russia, 1989–1996: A view with period cohort_fertility_tables.htm. al. Fertility, family planning, and parity-progression ratios. Genus 8. Preston SH, Heuveline P, Guillot M. women’s health: New data from the 55(3–4):11–60. 1999. Demography: Measuring and modeling 1995 National Survey of Family 36. Barkalov NB, Dorbritz J. European population processes. Oxford, UK: Growth. National Center for Health parity-progression-patterns: Results of Blackwell Publishers Ltd. 2001. Statistics. Vital Health Stat 23(19). the Fertility and Family Survey. 9. U.S. Census Bureau. Test of birth 1997. Z Bevolkerungswiss 30(2–3):175–218. registration completeness 1964 to 1968. 23. Ryder NB, Westoff CF. Reproduction in 2005. 1970 Census of Population and the United States 1965. Princeton, NJ: 37. Billari FC, Liefbroer AC, Philipov D. Housing PHC(E) No. 2. Evaluation and Princeton University Press. 1971. The postponement of childbearing in Research Program. Washington, DC: 24. Lorenz MO. Methods of measuring the Europe: Driving forces and U.S. Department of Commerce. 1973. concentration of wealth. Publications of implications. Vienna Yearb Popul Res 10. Sheps MC, Menken JA. Mathematical the American Statistical Association 1–17. 2006. models of conception and birth. 9(70):209–19. 1905. 38. U.S. Census Bureau. CPS historical Chicago, IL: The University of Chicago 25. Duncan OD. The measurement of time series tables. Table A-1. Press. 1973. population distribution. Popul Stud Washington, DC: U.S. Department of 11. French FE, Bierman JM. Probabilities 11(1):27–45. 1957. Commerce. 2010. of fetal mortality. Public Health Rep 26. U.S. Census Bureau. Historical 39. Philipov D, Liefbroer AC, Billari FC 77:835–47. 1962. statistics of the United States, colonial (eds). Postponement of childbearing in 12. Lesthaeghe R, Page H. Breastfeeding times to 1957. Washington, DC: U.S. Europe. Special edition. Vienna Yearb patterns in Nepal. An illustrative Department of Commerce. 1960. Popul Res. 2006. analysis. World Fertility Survey. 27. Petersen W. Population, 3rd edition. 40. Hamilton BE, Martin JA, Ventura SJ. London. 1980. London, UK: Macmillan Publishing Births: Preliminary data for 2009. 13. Jain A, Sivin I. Life table analysis of Company, Inc. 1975. National vital statistics reports; vol 59 IUDs: Problems and recommendations. 28. Ventura SJ. Trends and variations in no 3. Hyattsville, MD: National Center Stud Fam Plann 8(2):25–47. 1977. first births to older women, 1970–86. for Health Statistics. 2010. 14. Ford K. Socioeconomic differentials National Center for Health Statistics. 41. Hamilton BE, Cosgrove CM. Technical and trends in the timing of births. Vital Health Stat 21(47). 1989. appendix to the cohort fertility tables National Center for Health Statistics. 29. Lesthaeghe R. The second demographic for all, white, and black women: United Vital Health Stat 23(6). 1982. transition in Western countries: An States, 1960–2005. Internet tables. 15. Bramlett MD, Mosher WD. interpretation. In: Oppenheim-Mason K, Hyattsville, MD: National Center for Cohabitation, marriage, divorce, and Jensen AM (eds.). Gender and family Health Statistics. 2010. Available from: remarriage in the United States. change in industrialized countries. http://www.cdc.gov/nchs/nvss/ National Center for Health Statistics. Oxford, UK: Clarendon Press. 1995. cohort_fertility_tables.htm. Vital Health Stat 23(22). 2002. 30. Bureau of Labor Statistics. Changes in 42. Whelpton PK. Cohort fertility: Native 16. Schneider MC, Castillo-Salgado C, men’s and women’s labor force white American women in the United Loyola-Elizondo E, Bacallao J, Mujica participation rates. The Editor’s Desk. States. Princeton, NJ: Princeton OJ, Vidaurre M, Alleyne GA. Trends in Washington, DC: U.S. Department of University Press. 1954. infant mortality inequalities in the Labor. 2007. Americas: 1955–1995. J Epidemiol 31. Williams L, Abma J, Piccinino LJ. The Community Health 56(7):538–41. 2002. correspondence between intention to 17. Schneider MC, Castillo-Salgado C, avoid childbearing and subsequent Bacallao J, Loyola E, Mujica OJ, fertility: A prospective analysis. Fam Vidaurre M, Roca A. Methods for Plann Perspect 31(5):220–7. 1999. measuring health inequalities (part III). 32. Martin SP. Diverging fertility among Epidemiol Bull 26(2):12–5. 2005. U.S. women who delay childbearing 18. Glick PC. A demographer looks at past age 30. Demography 37(4):523– American families. J Marriage Fam 33. 2000. 37(1):15–26. 1975. Series 2, No. 153 [ Page 13

Table 1. Maternity table for the 1910 birth cohort, by age of mother

Number of Number of Number of Number of Probability of Number of first births childless childless years expected giving birth to childless occuring to person-years person-years to remain Age of woman first child at women at women at lived at lived from childless from in years age x age x age x age x age x to age 50 age x to age 50

x qx lx bx Lx Tx ex 15...... 0.0118 100,000 1,180 99,410 1,343,336 13.43 16...... 0.0269 98,820 2,658 97,491 1,243,926 12.59 17...... 0.0507 96,162 4,875 93,724 1,146,435 11.92 18...... 0.0765 91,286 6,983 87,795 1,052,711 11.53 19...... 0.0961 84,303 8,102 80,252 964,917 11.45 20...... 0.1059 76,201 8,070 72,167 884,664 11.61 21...... 0.1104 68,132 7,522 64,371 812,498 11.93 22...... 0.1134 60,610 6,873 57,173 748,127 12.34 23...... 0.1140 53,737 6,126 50,674 690,954 12.86 24...... 0.1092 47,611 5,199 45,011 640,280 13.45 25...... 0.1030 42,412 4,368 40,227 595,269 14.04 26...... 0.0963 38,043 3,664 36,212 555,041 14.59 27...... 0.0747 34,380 2,568 33,096 518,830 15.09 28...... 0.0692 31,812 2,201 30,711 485,734 15.27 29...... 0.0638 29,610 1,889 28,666 455,023 15.37 30...... 0.0568 27,721 1,575 26,934 426,357 15.38 31...... 0.0494 26,147 1,292 25,501 399,424 15.28 32...... 0.0417 24,855 1,036 24,337 373,923 15.04 33...... 0.0366 23,818 872 23,383 349,586 14.68 34...... 0.0305 22,947 700 22,597 326,204 14.22 35...... 0.0252 22,247 561 21,966 303,607 13.65 36...... 0.0203 21,686 440 21,466 281,641 12.99 37...... 0.0162 21,246 344 21,074 260,174 12.25 38...... 0.0126 20,902 263 20,770 239,101 11.44 39...... 0.0164 20,638 338 20,469 218,331 10.58 40...... 0.0117 20,300 238 20,181 197,861 9.75 41...... 0.0081 20,062 163 19,981 177,680 8.86 42...... 0.0050 19,900 99 19,850 157,699 7.92 43...... 0.0033 19,800 65 19,768 137,849 6.96 44...... 0.0019 19,735 37 19,716 118,081 5.98 45...... 0.0010 19,698 20 19,688 98,365 4.99 46...... 0.0005 19,678 10 19,673 78,677 4.00 47...... 0.0000 19,668 0 19,668 59,004 3.00 48...... 0.0000 19,668 0 19,668 39,336 2.00 49...... 0.0000 19,668 0 19,668 19,668 1.00

0.0000 Quantity more than zero but less than 0.00005. Page 14 [ Series 2, No. 153

Table 2. Maternity table for the 1935 birth cohort, by age of mother

x qx lx bx Lx Tx ex 15...... 0.0167 100,000 1,670 99,165 1,075,746 10.76 16...... 0.0349 98,330 3,432 96,614 976,581 9.93 17...... 0.0604 94,898 5,732 92,032 879,967 9.27 18...... 0.0879 89,166 7,838 85,248 787,934 8.84 19...... 0.1116 81,329 9,076 76,791 702,687 8.64 20...... 0.1279 72,252 9,241 67,632 625,896 8.66 21...... 0.1376 63,011 8,670 58,676 558,264 8.86 22...... 0.1440 54,341 7,825 50,428 499,588 9.19 23...... 0.1483 46,516 6,898 43,067 449,160 9.66 24...... 0.1497 39,618 5,931 36,652 406,093 10.25 25...... 0.1469 33,687 4,949 31,213 369,441 10.97 26...... 0.1401 28,738 4,026 26,725 338,228 11.77 27...... 0.1257 24,712 3,106 23,159 311,503 12.61 28...... 0.1095 21,606 2,366 20,423 288,344 13.35 29...... 0.0927 19,240 1,784 18,348 267,922 13.93 30...... 0.0776 17,456 1,355 16,779 249,573 14.30 31...... 0.0652 16,102 1,050 15,577 232,794 14.46 32...... 0.0529 15,052 796 14,654 217,218 14.43 33...... 0.0449 14,256 640 13,936 202,564 14.21 34...... 0.0379 13,616 516 13,358 188,628 13.85 35...... 0.0336 13,100 440 12,879 175,271 13.38 36...... 0.0285 12,659 361 12,479 162,391 12.83 37...... 0.0245 12,299 301 12,148 149,912 12.19 38...... 0.0200 11,997 240 11,877 137,764 11.48 39...... 0.0131 11,757 154 11,680 125,887 10.71 40...... 0.0072 11,603 84 11,562 114,207 9.84 41...... 0.0048 11,520 55 11,492 102,645 8.91 42...... 0.0036 11,464 41 11,444 91,153 7.95 43...... 0.0024 11,423 27 11,410 79,709 6.98 44...... 0.0012 11,396 14 11,389 68,300 5.99 45...... 0.0000 11,382 0 11,382 56,911 5.00 46...... 0.0000 11,382 0 11,382 45,528 4.00 47...... 0.0000 11,382 0 11,382 34,146 3.00 48...... 0.0000 11,382 0 11,382 22,764 2.00 49...... 0.0000 11,382 0 11,382 11,382 1.00

0.0000 Quantity more than zero but less than 0.00005. Series 2, No. 153 [ Page 15

Table 3. Maternity table for the 1960 birth cohort, by age of mother

x qx lx bx Lx Tx ex 15...... 0.0181 100,000 1,810 99,095 1,363,438 13.63 16...... 0.0312 98,190 3,064 96,658 1,264,343 12.88 17...... 0.0467 95,126 4,442 92,905 1,167,685 12.28 18...... 0.0591 90,684 5,359 88,004 1,074,779 11.85 19...... 0.0706 85,325 6,024 82,313 986,775 11.56 20...... 0.0793 79,301 6,289 76,156 904,462 11.41 21...... 0.0810 73,012 5,914 70,055 828,306 11.34 22...... 0.0824 67,098 5,529 64,334 758,251 11.30 23...... 0.0820 61,569 5,049 59,045 693,917 11.27 24...... 0.0841 56,521 4,753 54,144 634,872 11.23 25...... 0.0885 51,767 4,581 49,477 580,728 11.22 26...... 0.0918 47,186 4,332 45,020 531,252 11.26 27...... 0.0966 42,854 4,140 40,784 486,232 11.35 28...... 0.0994 38,714 3,848 36,790 445,447 11.51 29...... 0.0997 34,866 3,476 33,128 408,657 11.72 30...... 0.0975 31,390 3,061 29,860 375,529 11.96 31...... 0.0892 28,330 2,527 27,066 345,669 12.20 32...... 0.0808 25,803 2,085 24,760 318,603 12.35 33...... 0.0718 23,718 1,703 22,866 293,843 12.39 34...... 0.0645 22,015 1,420 21,305 270,976 12.31 35...... 0.0567 20,595 1,168 20,011 249,672 12.12 36...... 0.0498 19,427 967 18,943 229,661 11.82 37...... 0.0420 18,460 775 18,072 210,717 11.42 38...... 0.0342 17,684 605 17,382 192,645 10.89 39...... 0.0265 17,080 453 16,853 175,263 10.26 40...... 0.0212 16,627 352 16,451 158,410 9.53 41...... 0.0149 16,274 242 16,153 141,960 8.72 42...... 0.0101 16,032 162 15,951 125,806 7.85 43...... 0.0063 15,870 100 15,820 109,855 6.92 44...... 0.0038 15,770 60 15,740 94,035 5.96 45...... 0.0026 15,710 41 15,690 78,295 4.98 46...... 0.0013 15,669 20 15,659 62,606 4.00 47...... 0.0000 15,649 0 15,649 46,947 3.00 48...... 0.0000 15,649 0 15,649 31,298 2.00 49...... 0.0000 15,649 0 15,649 15,649 1.00

0.0000 Quantity more than zero but less than 0.00005. Page 16 [ Series 2, No. 153 Appendix. Technical Notes

Sources of Data The year begins exactly at a woman’s Number of years expected to remain birthday and concludes when she reaches childless from age x to the end of the The birth probabilities shown in this her next birthday (Figure 1 and reproductive period—Is parallel to the report were obtained from ‘‘Cohort Tables 1–3, column qx). These proba ‘‘life expectancy’’ function in a Fertility Tables for All, White, and bilities permit the calculation of the other mortality-oriented life table. However, Black Women: United States, functions in the maternity tables. instead of average number of years of 1960–2005’’ (7), ‘‘Fertility Tables for Cumulative percentage of having a life expected to live in the future, this Birth Cohorts by Color, United States, first birth at age x—Calculated by function estimates the average number 1917–1973’’ (4), and ‘‘Vital Statistics of subtracting the number of women who of years a woman expects to remain the United States, 1974’’ and for have had a first birth and dividing the childless from a specific age to the end 1999 (5,6). difference by 100,000 (using column lx of her reproductive period. For example, The ‘‘Cohort Fertility Tables for in Tables 1–3). This function is the women at age 15 in the 1910 birth All, White, and Black Women: United fundamental in the development of cohort may expect, on the average, to States, 1960–2005’’ (7) were recently cohort fertility analysis. Whelpton (42) remain childless for 13.4 years; that is, a released as a revision and extension of relied on this function for short- to woman can expect to have her first birth the cohort fertility measures (central medium-range fertility projections. by age 28.4. While some women will birth rates, cumulative birth rates, parity Cumulative percentage of first births at remain childless to the end of their distributions, and birth probabilities) ages 18, 22, and 40 provided robust reproductive period, the majority will published in the other, older reports. estimates of final childlessness. give birth before then (Figure 5 and Detailed information on the computation As noted, not all women have a Tables 1–3, column ex). of birth probabilities and the other first birth in their lifetimes. Accordingly, The Lorenz (concentration) measures may be found in the the cumulative probability of having had curve—Included to show the ‘‘Technical Appendix to the Cohort at least one (first) birth by the end of concentration of first births by age. The Fertility Tables for All, White, and the reproductive period is approximately graph illustrates the dispersion of first Black Women: United States, 80 percent to 90 percent (Figure 2). births over the range of the reproductive 1960–2005’’ (41). Number of the birth cohort lives of women rather than the central remaining childless—Focuses on how tendency of first births over the range Description of Life long a cohort of women stay in the state (e.g., the average age of first birth). In Table Functions of childlessness. The maternity tables in this, the Lorenz curve permits the this report use a standard 100,000 as the measure of skewness or ‘‘tilt’’ of the Age of woman (x)—Identifies the number of childless women who enter first-birth curve. The women in the 1935 cohort with the year of the date on the table at the beginning of their cohort were considered to be young which the woman’s birth occurred. reproductive lives. Each year some when they had their first births, whereas Because these women retain this women give birth, which decreases the the members of the 1960 cohort, by designation throughout their size of the remaining childless cohort. comparison, were much older. childbearing years, there is a fixed This function depicts the size of the Figure 6 shows Lorenz curves in relationship between the cohort childless population at any given age addition to a diagonal line at 45 degrees, identification year, the age of the (up to age 50). As noted, not all women which indicates an even distribution of member of the cohort (column x), and give birth in their lifetimes. Related to the births by age. The further the Lorenz the calendar or data year to which the complement of the previous measure, curve deviates from the 45-degree fertility measure refers. 10 percent to 20 percent of women in the diagonal line, the more concentrated is Probability of giving birth to a first birth cohorts remained childless (Figure 3 the age distribution of first births. If the child at age x—Indicates the probability and Tables 1–3, column lx). number of first births was equal in each or chance that a childless woman Number of first births occurring to age group—that is, the distribution changes her status to being a mother women at age x—Shows the number of curve lies on the diagonal line—the within a specific year and is the single first births occurring within a given age distribution curve would represent a most important function in the maternity interval. The number of first births is complete lack of concentration. If all table. The transition from being influenced by the size of the pool of first births took place in a single age childless to being a mother is the first childless women, the percentage of interval, the distribution curve would and, obviously, most important step in a women in a sexual relationship in that represent the maximum, or 100 percent, woman’s fertility career (31), affecting pool, and the probability of giving birth concentration of births at one age. Two nearly all social, economic, and to a first child for members of that age measures of concentration related to the emotional aspects of a woman’s life. class at risk of childbearing (Figure 4 Lorenz curve discussed in this report are and Tables 1–3, column bx). the Gini Concentration Ratio and the Series 2, No. 153 [ Page 17

Duncan Index of Concentration. birth in year y, 0 qi,y, Numerically, the Duncan index is 1 where BRi,y = first-order central birth rate of different from the Gini index as the 0 women at age i in year y, q = probability that a first birth Duncan is affected by the number of and occurs within 1 year, age classes. 0 i = age of woman, Distribution of children ever born, PDi,y = proportion of childless women or parity, by birth cohort—Refers to a at age i in year y. and distribution of all women in a cohort by y = year The formulae for computing the the number of children ever born alive birth probabilities of higher parities (See general formula for probability of to those women up to a specified (one, two, three, four, five, six, seven, birth, q , above.) age—generally up to age 49. The n i or higher), as well as the computed proportions may be expressed on a per Age- and cohort-specific number of probabilities, are available 1,000 basis (per mille, for greater childless women at ages 15–49—Refers elsewhere (41). precision) (Figure 7), or as a percentage to the number of women at age i from Note that the probabilities shown in (Figure 8) (4,7). This measure is the original cohort who have yet to have Tables 1–3 are specific to those women important to describe the household, any children at the beginning of year y. born in 1910, 1935, and 1960 ‘‘at risk’’ which may be large or small, and to of having their first birth. As mentioned, l 0 , describe at what ages women give birth i,y the probabilities show the likelihood of and in which various orders. where first birth between the beginning of an Cohort total fertility rate 0 age interval and before reaching the end l = the number of women who (TFR)—Refers to the average completed of that age interval. For example, the have not had any children, fertility of women in a cohort probability of a first birth for women in i = age of woman, (Figure 9). It takes into account the the 1960 cohort in the age interval cumulative fertility rates over all ages, and 20–21 is 0.0793 (Table 3). This means not just the rate of first births. This that for every 1,000 women who reach y. = year summary indicator is not included in the their 20th birthday without having given 0 0• 0 maternity table, but is used in this report li+l,y = li,y qi+l,y birth, 79.3 of them will give birth before to show the impact of childlessness reaching their 21st birthday. (Often the cohort is set to have an initial relative to completed fertility of a It is assumed that births are evenly magnitude like 100,000.) cohort (4,7). The TFR based on the distributed across the single-year age cohort fertility data is considered to be Age- and cohort-specific number of interval under consideration. Across age, the ‘‘truer’’ measure of fertility than the first-born children for women at ages the probability of first birth rises with TFR based on period data; the latter is 15–49—Refers to the number of first age of mother, peaking sometime in the complicated by the overlap in timing of births occurring to women, at age i, 20s, and then declines. The probability cohort rates. within year y. of dying, in comparison, generally 0 increases with age. This is an important bi,y , General Probability of distinction for the final age group in the where life tables. With traditional mortality- 0 Birth (nqx) b = the number of first-born related life tables, everybody within this children, The probability of birth estimates age group dies; that is, the probability of the likelihood that a woman who has i = age of woman, dying equals one ( nqx = 1.000). attained parity n (either zero, one, two, However, the probability of first birth and three, four, five, six, seven, or higher) for the final age group of the birth y = year. by age i will have another (n + 1)th cohort is less than one, so that some b0 = q0• l 0 birth before reaching the end of that age women remain childless throughout i,y i,y i,y interval; that is, before age i + 1. The their lives. Age- and cohort-specific number of birth probabilities are computed using childless years for women at ages the central birth rates and the parity Short Definitions of Life 15–49—Refers to the number of distributions (41). childless years lived by women at age i The formula for the probability of Table Functions and in year y, taking into account the zero parity—that is, women having their Formulae decrease of childless women as the first birth—is: cohort ages in the year. Age- and cohort-specific, parity BP 0 = BR 1/ PD 0 • 1,000.0, i,y i,y i,y zero, birth probabilities for women at 0 Li,y , where ages 15–49—Refers to the probability where or chance that a childless woman, at age 0 0 BPi,y = probability of a childless L = i, will have a first birth within the year. i,y the number of childless years woman at age i having a live lived by childless women at age i Page 18 [ Series 2, No. 153 and Cumulative birth rates—Refers to and 0 the sum of central fertility rates from Li,y = is calculated for all ages for B = the area under the line of each cohort. age 15 to the current age. equality. 0 • 0 • 0 CumBR, If the function is known, the ratio Li,y = (0.5) li,y + (0.5) li+l,y where may be easily found with integration. Cohort-specific number of years However, as when working with CumBRn = CenBRn + CumBRn childless from current age to age i+1,y+1 i,y i,y discrete points, the ratio can be 50—Refers to the number of childless i = age, approximated as follows: years from age i to the end of y = year, G =1–Σn (X –X ) • (Y + Y ), reproductive period. k=1 k k–1 k k–1 and 0 where Ti,y n = parity. X = horizontal point, where k To repeat, the TFR takes into 0 Yk = vertical point, Ti,y = the total number of childless account the cumulative fertility rates for years lived over exact age i by all parities, not just the rate for a birth and women in the cohort order one. (With the TFR, the emphasis k = sequence of each point. and is usually on rates for all ages.) Duncan Index of Concentration— T0 = Σ50 L , that is, the sum of Refers, geometrically, to the maximum i,y i=x x,y Indicators of Concentration childless women-years from vertical distance from the diagonal line of equality to the Lorenz curve. age x to age 50. Lorenz curve—Is a graphical Algebraically, the index is simply representation of various types of the sum of values of Age- and cohort-specific expected inequality, where the x axis represents number of years to be childless for the cumulative proportion of an |X –Y|. k k women at ages 15–49—Refers to the independent variable such as time, average number of years a woman at population, etc., and the cumulative As such, it is equivalent to the age i in year y expects to remain proportion on the y axis of a dependent Index of Dissimilarity, which is the sum childless. variable, such as income or, for this of the positive differences between the two percent distributions. The value of e0 , report, first births. The curve is convex, i,y and is graphed between 0.0 and 1.0. As the concentration index depends upon where an example, it could be said that a curve the size of the set of geographic units 0 e = the average number of years may show that 45 percent of the women used. expected to remain childless in the population had 70 percent of its Δ = Duncan Index of Concentration between ages x and 50, children. and i = the age of woman x, Gini Concentration Ratio—The graph containing the Lorenz curve also =½Σn |X –Y|, and k=1 k k holds a diagonal line at 45 degrees; that y where = year. is, where x = y. This line is called the X = horizontal point, 0 0 0 ‘‘line of perfect equality.’’ If the Lorenz k ei,y = Ti,y / li,y curve lies precisely on the diagonal line, Yk = vertical point, Cohort TFR—Refers to the average then all members of the horizontal axis and have an equal distribution on the y axis. completed fertility of women in a given k = sequence of each point. birth cohort at the end of their A perfectly unequal distribution would The computation of the Duncan reproductive period. be one in which one person has the entire amount of the item measured and index provides the point where the TFR , y everyone else has none. concentration is greatest. It is calculated where Theoretically, the Gini ratio (G)isa by subtracting the individual values ratio of areas that lies between the line between the line of equality from the TFR = the average completed fertility of perfect equality and the Lorenz curve Lorenz curve. Its largest value indicates of women in a cohort at age 50 to total area under the line of equality. the age at greatest concentration. and G = A/B, TFR = Σ8+ CumBR is the sum of y n=1 i,y where cumulative birth rates from A = the area between the line of parity one to eight or higher. perfect equality and the Lorenz curve Vital and Health Statistics Series Descriptions

ACTIVE SERIES DISCONTINUED SERIES

Series 1. Programs and Collection Procedures—This type of report Series 4. Documents and Committee Reports—These are final describes the data collection programs of the National Center reports of major committees concerned with vital and health for Health Statistics. Series 1 includes descriptions of the statistics and documents. The last Series 4 report was methods used to collect and process the data, definitions, and published in 2002. As of 2009, this type of report is included other material necessary for understanding the data. in Series 2 or another appropriate series, depending on the report topic. Series 2. Data Evaluation and Methods Research—This type of report concerns statistical methods and includes analytical Series 5. International Vital and Health Statistics Reports—This techniques, objective evaluations of reliability of collected type of report compares U.S. vital and health statistics with data, and contributions to statistical theory. Also included are those of other countries or presents other international data of experimental tests of new survey methods, comparisons of relevance to the health statistics system of the United States. U.S. methodologies with those of other countries, and as of The last Series 5 report was published in 2003. As of 2009, 2009, studies of cognition and survey measurement, and final this type of report is included in Series 3 or another series, reports of major committees concerning vital and health depending on the report topic. statistics measurement and methods. Series 6. Cognition and Survey Measurement—This type of report Series 3. Analytical and Epidemiological Studies—Thistypeof uses methods of cognitive science to design, evaluate, and report presents analytical or interpretive studies based on vital test survey instruments. The last Series 6 report was and health statistics. As of 2009, Series 3 also includes published in 1999. As of 2009, this type of report is included studies based on surveys that are not part of continuing data in Series 2. systems of the National Center for Health Statistics and Series 12. Data From the Institutionalized Population Surveys— international vital and health statistics reports. The last Series 12 report was published in 1974. Reports Series 10. Data From the National Health Interview Survey—This from these surveys are included in Series 13. type of report contains statistics on illness; unintentional Series 14. Data on Health Resources: Manpower and Facilities— injuries; disability; use of hospital, medical, and other health The last Series 14 report was published in 1989. Reports on services; and a wide range of special current health topics health resources are included in Series 13. covering many aspects of health behaviors, health status, and health care utilization. Series 10 is based on data collected in Series 15. Data From Special Surveys—This type of report contains this continuing national household interview survey. statistics on health and health-related topics collected in special surveys that are not part of the continuing data Series 11. Data From the National Health Examination Survey, the systems of the National Center for Health Statistics. The last National Health and Nutrition Examination Surveys, and Series 15 report was published in 2002. As of 2009, reports the Hispanic Health and Nutrition Examination Survey— based on these surveys are included in Series 3. In this type of report, data from direct examination, testing, and measurement on representative samples of the civilian Series 16. Compilations of Advance Data From Vital and Health noninstitutionalized population provide the basis for (1) Statistics—The last Series 16 report was published in 1996. medically defined total prevalence of specific diseases or All reports are available online, and so compilations of conditions in the United States and the distributions of the Advance Data reports are no longer needed. population with respect to physical, physiological, and Series 22. Data From the National Mortality and Natality Surveys— psychological characteristics, and (2) analyses of trends and The last Series 22 report was published in 1973. Reports relationships among various measurements and between from these sample surveys, based on vital records, are survey periods. published in Series 20 or 21. Series 13. Data From the National Health Care Survey—This type of Series 24. Compilations of Data on Natality, Mortality, Marriage, and report contains statistics on health resources and the public’s Divorce—The last Series 24 report was published in 1996. use of health care resources including ambulatory, hospital, All reports are available online, and so compilations of reports and long-term care services based on data collected directly are no longer needed. from health care providers and provider records. Series 20. Data on Mortality—This type of report contains statistics on For answers to questions about this report or for a list of reports published mortality that are not included in regular, annual, or monthly in these series, contact: reports. Special analyses by cause of death, age, other Information Dissemination Staff demographic variables, and geographic and trend analyses National Center for Health Statistics are included. Centers for Disease Control and Prevention Series 21. 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CS222867 DHHS Publication No. (PHS) 2011–1353, Series 2, No. 153