Life-Span Age Trends in Laterality1

Journal of Gerontology 1980, Vol. 35, No. 5, 715-721

Life-span Age Trends in Laterality1

Clare Porac, PhD2, Stanley Coren, PhD3, and Pam Duncan, PhD2

Laterality of hand, foot, eye, and ear was measured in a sample of 1964 subjects, ranging in age from 8 to 100 years. Age trends were found, with hand, foot, and eye preference becoming more right-sided and ear preference becoming more left-sided with increasing age. Sex differences emerged in foot, eye, and ear preference but these did not systematically interact with the age variable. Several causal mechanisms are proposed but none can fully explain either the direction or the magnitude of the observed age changes. Thus, these data are most consistent with the view that the study of sidedness in humans should proceed with a consideration of a complex of underlying factors and individual difference variables. Key Words: Laterality, Sex differences, Age differences, Life-span, Handedness

ESPITE the fact that the human body Corballis & Morgan, 1978; Levy, 1977; Morgan D appears to be bilaterally symmetrical, & Corballis, 1978). Some researchers have there are distinct asymmetries in how the used this fact to argue that sidedness has a paired limbs and sensory organs are used. The physiological or even a genetic basis and is most obvious dimension of laterality is hand linked to asymmetries in brain development preference. Approximately 90% of all humans and neural control. Other investigators have consistently use the right hand in coordinations maintained that the preponderance of right- where only one hand can be used (such as sidedness within populations indicates an writing or throwing a ball). There is an anal- environmental influence related to the evolu- ogous dimension of foot preference. Thus most tion of tool use or cultural patterns towards individuals prefer to kick a ball with the right confirmity to the majority (Blau, 1946; Collins, foot. Less obvious asymmetries in lateral 1977; Dawson, 1977; Hildreth, 1949). It is in preference are found for the eyes and ears. the context of this controversy that the study These are displayed in such tasks as sighting of age-related changes in lateral preference down a telescope or pressing an ear against behaviors assumes some importance. For in- a clock to hear its faint ticking. As in laterality stance, the absence of any age trends would of the limbs, there is a consistent tendency be difficult to explain if one felt that lateral to prefer the sense organ on the right side in preference behaviors Were primarily based such coordinations (Clark, 1957; Porac & upon the cumulative effect of environmental Coren, 1979). pressures. Lateral preference behaviors have en- There have been a number of attempts to gendered scientific interest for centuries. The assess age trends in handedness. These studies fact that these coordinations, especially hand- generally report that individuals become more edness, show a strong right-sided, or dextral, right-handed with increasing chronological age bias in one of the aspects of the problem that (Fleminger et al., 1977; Hildreth, 1949). The has caused considerable debate and theoretical lateralities of foot, eye, and ear have not been controversy (Annett, 1973; Collins, 1977; systematically studied in this way, which is unfortunate, since investigations of the changes •This research was supported by grants from the Natural Sciences and in other aspects of laterality can also con- Engineering Research Council of Canada and the Medical Research Council of Canada. We would like to thank A. R. Hakstian and J. Lynd for tribute to our understanding of human sided- their statistical advice and consultation. Requests for reprints and/or the list of studies used to tabulate Table 1 and Fig. 2 should be sent to C. Porac, Dept. ness and, perhaps, help to resolve some of the of Psychology, Univ. of Victoria, Victoria, B.C., V8W 2Y2, Canada. current theoretical controversy. Life-span 2Dept. of Psychology, Univ. of Victoria, Victoria, B.C., V8W 2Y2, Canada. trends for foot and eye, as well as for hand 3Dept. of Psychology, Univ. of British Columbia, Vancouver, B.C., V6T 1W5, Canada. preference, are suggested when one surveys

715

Downloaded from https://academic.oup.com/geronj/article-abstract/35/5/715/533241 by McGill University Libraries user on 05 November 2017 716 PORAC, COREN AND DUNCAN

the existing literature on the topic of laterality. All were middle class Caucasians residing in Many investigators have studied lateral prefer- urban areas of the U.S.A. and Canada. Sub- ence in samples of different ages. By tabulat- jects were contacted through the assistance ing the incidence of right-sidedness reported of educational institutions, recreation associ- in a number of these studies, one can crudely ations, and associations for retired persons. assess the possibility of age trends. The results Only non-institutionalized individuals with full of such a tabulation are shown in Table 1 which use of both hands, feet, eyes, and ears were summarizes the data from 113 studies pub- included in the sample. Since sex differences lished during the past 90 years. The criterion in the measurement of handedness and eyed- for inclusion in this survey was the use of a ness have been reported (Bryden, 1977; Porac preference measure to assess handedness, & Coren, 1975), care was taken to ensure an footedness, or eyedness (unfortunately, there approximately equal proportion of males and are too few studies of ear preference to make females, especially in the most senior age meaningful age comparisons). The data in groups where sex differences in mortality Table 1 suggest age trends for hand, eye, and rates could lead to an over-representation of foot preference. The pattern is similar in each females in this portion of the sample. The instance with adults seeming to be more dextral final representation of sex within each age group than children. These data are only suggestive was 43% male in the 8 to 15 year range, 59% of life-span trends. Each of the studies sur- in the 16 to 25, 58% in the 26 to 35, 51% in the veyed used different measures of lateral prefer- 36 to 45, 52% in the 46 to 55, 41% in the 56 to ence, and the age groupings vary and are un- 65, 52% in the 66 to 75 and 54% in the 76 to evenly spaced. However, the suggestion that 100 year group. there are age trends in lateral preference over the life span does warrant further systematic Measurement of lateral preference. — Lat- study. The present report attempts to.assess eral preference was measured by means of a changes in hand, eye, foot, and ear preference 13-term behaviorally-validated self-report over the age range from 8 to 100 years. battery. There were four questions concern- ing hand use and three questions each for the METHOD assessment of foot, eye, and ear preference. Individuals were permitted a choice of three Subjects. — The sample consisted of 1964 possible responses to each question, "right," subjects, ranging in age from 8 to 100 years. "left," or "both." The questions used appear

Table 1. Age Trends in Hand, Foot and Eye Preference Based upon a Survey of 113 Published Studies.

Type of Approximate Age No. of Studies % Right-Sided Behavior Preference Range Studied Reviewed Mean S.D. Hand Infant 3 79.9 14.1 , Pre-School 4 82.6 9.4 Elementary School 24 92.7 4.5 High School/College 15 90.0 4.7 Adult 20 92.3 3.4 Foot Infant Pre-School — — — Elementary School 6 84.6 12.8 High School/College 4 64.7 15.1 Adult 3 90.5 7.1 Eye Infant 1 62.0 Pre-School 3 60.5 7.0 Elementary School 18 65.6 6.5 High School/College 9 69.6 4.3 Adult 15 71.0 6.7 Note: Some studies are represented under 2 or 3 categories. Thus the number of distinct contributions to the table is 113.

Downloaded from https://academic.oup.com/geronj/article-abstract/35/5/715/533241 by McGill University Libraries user on 05 November 2017 AGE AND LATERALITY 717

in other published reports and each of them has 0 score constituted less than 1% of the sample) been validated against actual performance were classified with the left group. For both measures in three separate studies (Coren & types of scoring, the age range was subdivided Porac 1978; Coren et al., 1979; Raczkowski into 10-year blocks except for the youngest et al., 1974). They have an average concord- (8 to 15 years) and the oldest (76 to 100 years) ance rate of 90% with direct behaivoral mea- age group. The combination of the oldest age sures of hand, foot, eye, and ear performance categories was done to insure that no age (Coren et al., 1979). grouping contained fewer than 50 individuals.

RESULTS Analysis of age trends. The results derived The data were scored in two ways. The first from the dichotomous scoring procedure are involved a numerical tabulation of the self- shown in Fig. 1 which plots the mean percent- report responses for each index of laterality, age of right-sidedness as a function of age for assigning a +1 for each response of "right," each of the four indices of laterality. Dextrality a -1 for each response of "left," and a 0 for is the norm regardless of age on any one of each response of "both." The algebraic sum the four dimensions of lateral preference. This of all of the responses for each index gave the is consistent with the reports summarized respondent's score. Thus the composite score in Table 1. However, the proportion of the incorporates both the direction and the con- sample classified as right-handed, right-footed, sistency of laterality, with higher numbers or right-eyed increases with chronological indicating greater dextrality. In the second age. Conversely, the percentage of the sample procedure, individuals were dichotomously classified as right-eared decreases with age, classified with sums greater than 0 scored as although dextrality still predominates even in right-sided. Thus, individuals with no clear the oldest age group. Table 2 contains the left or right preference (respondents with a mean score for each age group on the four

Table 2. Mean Lateral Preference Scores H- HAND for Each Index and Age Group.a 100 E=EYE A=EAR I Age CD (Years) N Hand Foot Eye Ear Q: 90 8- 15 282 2.68 1.67 1.15 1.00 (2.37) (1.73) (2.37 (2.16) 16-25 396 2.94 1.59 1.17 0.69 Q (2.08) (1-57) (2.22) (2.11) rr 80- 26-35 392 2.89 1.60 1.36 0.63 (2.35) (1-82) (2.27) (2.35) i/) 36-45 243 3.03 1.75 1.74 0.22 _i (2.20) (1.66) (2.03) (2.40) o y \ E E/ 46-55 317 3.33 2.05 1.51 0.41 A (1.70) (138) (2.20) (2.39) LU 56-65 189 3.35 2.11 1.27 0.44 O A (1.52) (1.42) (2.31) (2.41) 60 .V 66-75 84 3.30 2.06 1.26 0.30 LU (1.42) (1-41) (2.20) (2.20) o LU 76-100 61 3.78 2.22 1.70 0.93 cr 50 / (0.70) (1.28) (2.05) (2.51) I I Combined 1964 3.03 1.78 1.35 0.58 10 20 30 £0 50 60 70 80 (2.07) (1.62) (2.24) (2.30) Maximum Right Score 4 3 3 3 Maximum Left Score -4 -3 -3 -3 Fig. 1. The percentage of the sample classified as right- ssidei d as a function of chronological age, for hand, foot, Note: aStandard deviations arc: shown in parentheses. eeye, and ear preference.

Downloaded from https://academic.oup.com/geronj/article-abstract/35/5/715/533241 by McGill University Libraries user on 05 November 2017 718 PORAC, COREN AND DUNCAN

indices of preference; it also clearly shows a The slopes of the regression lines will then systematic shift in lateral preference scores as approximate the rate of change with age for a function of age. each preference type. These dextral shifts are Previous evidence has suggested that the 0.19% per year for handedness, 0.15% per indices of laterality are correlated within in- year for footedness, and 0.07% for eyedness. dividuals (Porac & Coren, 1979). The obtained For earedness, the shift is toward the left, at correlations for the present sample are shown a rate of about 0.07% per year; however, if in Table 3. Since all are significant (p < .001), one considers only the first 40 years, the left- MANOVA analyses were conducted to assess ward shift occurs at a rate of 0.45% a year. the nature and significance of these apparent While these age changes in lateral preference age trends. A two-way MANOVA (age by sex) may not seem very large, they accumulate revealed a significant effect of age across the into a substantial change over the lifespan. four indices of lateral preference, Wilkes Thus, for example, there are 14.5% more right- Lambda (4,7,1948) = .949, F = 3.67, p < .001. handers in the oldest as opposed to the young- However, the overall significance of the est age group. MANOVA does not specify the nature of the existing group differences. Since there were no Analysis of sex differences. — Although the significant age by sex interactions, data were variables of sex and age did not interact, the collapsed across sex and a profile analysis was overall MANOVA did reveal a main effect for conducted. It indicated that the obtained age sex, Wilkes Lambda (4,1, 1948) = .960, trends were not parallel, Maximum root = F = 20.41, p < .001. The nature of these sex .031, df = 3, 1.5, 976, p < .0001, suggesting differences can be seen in Fig. 2 where the that the different laterality indices show dif- percentage of individuals classified as right- ferent age trends. To decompose these effects, sided on each index of laterality is graphed individual analyses were conducted on all separately for males and for females. There four forms of lateral preference. are no significant sex differences in handed- The effect of age was significant for all four preference indices in the succeeding univariate analyses, with F(7,1956) = 3.93,/? < .001, for handedness; F(7,1956) = 4.80, p < .0001, for footedness;F(7,1956) = 2.16,/? < .05, foreyed- ness; and F(7,1956) = 3.05,/? < .01, for earedness. In addition, all of the tests for a linear trend reached significance: F(l,1956) = 23.86, p < .0001, for handedness; F( 1,1956) = 25.50, p < .0001, for footedness;F( 1,1956) = 11.26, K) 20 30 10 50 60 70 10 20 30 i.0 50 60 70 80 p < .001, for earedness; and F(l,1956) = 4.11, AGE AGE p < .05, for eyedness (this last being the weak- est trend of the four). Ear preference also showed a significant quadratic component, F(l,1956) = 6.37,/? < .05. None of the higher- order trend analyses was significant for the other three indices. Thus, one may summarize these results as showing relatively linear age '—AW trends for laterality of limbs and sense organs. Hand, foot, and eye preference become more v

right-sided with increasing age while ear pref- 10 20 30 tO 50 60 70 60 erence shifts towards the left side in a some- 20 30 1.0 50 60 70 what non-linear fashion with the greatest AGE AGE change in the first four decades of life, after which an asymmptotic level is reached.

One can attempt to quantify the rate at which Fig. 2. The percentage of males and females classified lateral preference changes by computing best- as right-sided on each of the four indices of lateral fitting linear regressions for the data in Fig. 1. preference.

Downloaded from https://academic.oup.com/geronj/article-abstract/35/5/715/533241 by McGill University Libraries user on 05 November 2017 AGE AND LATERALITY 719

ness (Fig. 2A), but males are significantly shows the scatterplot of the reported per- more left-sided than females in footedness centage of right-handedness as a function of (Fig. 2B) and earedness (Fig. 2D). The F val- the date of publication of the study. The ob- ues are F( 1,1948) = 51.55,/? < .001, for footed- tained correlation between these two variables ness and F( 1,1948) = 17.34,/? <.001, for eared- is negative, as predicted by the social pressure ness. The opposite result was shown by the eye hypotheses (r = .28); however, it is not sta- preference responses (Fig. 2C) where females tistically significant. In addition, the slope of are significantly more left-eyed than males, the observed decrease in the reported inci- F(l,1948) = 6.15, p < .05. dence of dextrality is .05% which is only one- fourth of the rate of change revealed in the DISCUSSION handedness data in Fig. 1. Thus the overt social What are the causes of these systematic pressure hypothesis can only account for a shifts in right- and left-sidedness in lateral small portion of the observed change in preference? Several hypotheses are possible, handedness. There are no existing hypotheses both of a developmental and of a nondevelop- which suggest that overt social pressure has mental nature. A likely nondevelopmental been applied to foster certain types of foot, hypothesis is based upon changing attitudes eye, and ear preference. Thus it seems even toward left-handedness over the years. For less likely that this hypothesis can account for example, prior to about 1930, both psychol- the age trends obtained. ogists and educators favored the practice of Two developmental hypotheses seem to be shifting a child's writing hand from the left to somewhat more successful in explaining the the right side. There was a very strong nega- present findings. First, the existence of covert tive bias toward the use of the left hand for environmental pressures toward right-handed- writing during this era (cf. Blau, 1946). How- ness may be of sufficient magnitude and fre- ever, in succeeding years this attitude changed quency to gradually strengthen the develop- and, as a result, there are reports that the in- ment of right-sidedness throughout life. Every- cidence of left-handed writers has increased day instances of such covert pressures are easy (Hildreth, 1949; Levy, 1976). Since the present to find, especially for handedness. Left- data represents handedness responses from handers often complain about the right-handed several generations, it is possible that the biases which are built into many common 14.5% rise in the incidence of right-handedness mechanisms such as can openers, scissors, reflects the changing pattern of social pressures or power tools. Rightward biases also exist on the training of the writing hand which might in a less frequent form for footedness, in the then bias all hand preference behaviors. One arrangement of foot pedal controls in auto- way to test this hypothesis is to consider a mobiles and other machinery. Instances of number of normative studies of adult hand preference that have been conducted over the

span of years during which this shift in social 100 pressure has taken place. If overt pressure on the selection of the writing hand plays a role in determining the age trend observed in Fig. 1, the studies conducted earlier in this century should report higher proportions of dextral 90 individuals than those conducted more re- cently. To evaluate this possibility 34 studies published between 1913 and 1976 were re-

viewed. Since there have been occasional re- 80 ports of racial and cultural differences in the incidence of right-handedness (Dawson, 1977; 1910 1920 193930 1940 1950 1960 1970 1980 Teng et al., 1976), the review was restricted Year of Publication to studies using western, Caucasian adult samples. Only studies using preference mea- Fig. 3. The percentage of adults classified as right- sures (analogous to those employed in the handed in 34 studies as a function of the date of publication present investigation) were sampled. Fig. 3 of the report.

Downloaded from https://academic.oup.com/geronj/article-abstract/35/5/715/533241 by McGill University Libraries user on 05 November 2017 720 PORAC, COREN AND DUNCAN

such dextral biases may even be found for Table 3. Intercorrelations Between the Four eyedness in pieces of equipment which require Indices of Lateral Preference (N = 1964). sighting, such as rifles. Everyday experience with a dextral world may enhance right-sided Hand Eye Foot Ear performance, and such factors have been Hand .308 .538 .213 shown to be influential in the determination Eye — .262 .221 of hand (paw) preference in animals (Collins, Foot — .330 1975). These covert influences can account for Ear - the higher percentages of individuals who can be classified as right-handed, -footed, and -eyed in the older age groups. Integrating logical mechanism. However, this hypothesis the leftward shift in ear preference into this is weakened when one considers that other scheme is more difficult. However, one could measures of lateral asymmetry, such as per- interpret the ear preference data, not as a formance on dichotic listening tasks, do not leftward shift with age, but as a loss ofdextral- show consistent age trends (Hynd & Obrzut, ity and a regression toward an unbiased pop- 1977; Schulman-Galambos, 1977). In addition, ulation (equal numbers of right-and left-eared the existence of different trends for the vari- individuals) as a function of increasing age. ous indices of laterality seems to be most con- This interpretation is supported by the fact sistent with the hypothesis that more than one that the age groups from 8 to 35 show propor- physiological mechanism is responsible for tions of right-eared individuals in numbers manifestations of laterality. which are significantly greater than chance How can one incorporate the group dif- (z = 4.75,p < .01;z = 3.29,p < .01;z = 2.63, ferences between males and females on foot, p < .01, respectively); however, the propor- ear, and eye preference into this scheme? The tion of right-earedness does not exceed chance most commonly-reported form of sex differ- levels for the remaining age categories (z = ence in laterality, the finding that males are 0.06; z = 1.63; z = .65; z = .00; z = 1.35). more left-handed than females (Bryden, 1977) Perhaps the absence of environmental pres- is not confirmed in this study. However, these sures on right-ear use results in a gradual loss of data do support the results of Porac and Coren existing ear preferences with advancing age. (1975) who found greater degrees of right- Secondly, it is possible that the present trend eyedness in males. Regardless of the type represents developmental maturational pro- of hypothesis proposed to explain the age cesses. While most of the available data indi- changes, it is clear that males and females dis- cate that neural development and myelination play differing degrees of rightward bias on are complete by the end of the second decade three of the indices of lateral preference and of life (Flechsig, 1920), some reports have that these differences do not systematically indicated that myelination in parts of the cor- change with age. The existence of group gender tex may be incomplete until the age of 45 or differences, in addition to the age trends, later (Kaes, 1907) and that neural develop- supports the notion that the manifestations of ment in the cerebral commissures continues human sidedness are the results of complex into the third decade (Yakovlev & Lecours, processes that interact with at least two indi- 1967). If laterality is determined by a speech vidual difference variables. dominant cerebral hemisphere as some in- This study is clearly only a first step. Not vestigators maintain (Levy & Reid, 1978), only have life span changes in lateral prefer- then one might expect to find a single under- ence been virtually ignored, but data on age lying dimension of laterality with the present changes in footedness, eyedness, and eared- findings caused by neural maturation. Table ness are sparse. The present data suggest that 3 presents the Pearson product moment cor- lateral preference in limbs and sense organs relation coefficients between the various in- is not fixed but continues to change across the dices of lateral preference, and all are highly life span. This is of theoretical import and significant (p < .001). This fact could be taken must be taken into account in any attempt to as support for the notion that there may be a provide a comprehensive explanation of hu- single underlying dimension of lateral pref- man laterality. Certainly the notion that pat- erence primarily determined by one physio- terns of laterality are fixed and immutable

Downloaded from https://academic.oup.com/geronj/article-abstract/35/5/715/533241 by McGill University Libraries user on 05 November 2017 AGE AND LATERALITY 721

beyond childhood is not supported, although Flechsig, P. Anatomie des menschlichen gehirns and the mechanisms which promote the develop- ruckenmarks auf myelognetischer grundlage. Georg mental trends observed here are, at present, Thiem, Leipzig, 1920. Fleminger, J. J., Dalton, R., & Standage, K. F. Age as ambiguous. It is likely that a number of dif- a factor in the handedness of adults. Neuropsycho- ferent factors may determine and maintain logia, 1977, 15, 471-473. the complex of behaviors which lead to sided- Hildreth, G. The development and training of hand ness, or lateral preference in humans. More dominance, I-III. Journal of Genetic Psychology. 1949, 75, 197-275. direct experimental intervention and analysis Hynd, G. W., & Obrzut, J. E. Effect of grade level and of the patterns of interrelationships among sex on the magnitude of the dichotic ear advantage. the indices of lateral preference will be needed Neuropsychologia, 1977, 15, 689-692. to provide clearer answers. Kaes, T. Die Grossnirnrinde des menschen. Ein Gehir Anatomischer Atlas. Jena Verlag von Gustov Fischer, 1907. REFERENCES Levy, J. A review of evidence for a genetic component Annett, M. Handedness in families. Annals of Human in the determination of handedness. Behavior Genetics, Genetics. 1973, 37. 93-105. 1976, 6. 429-453. Blau, A. The master hand. American Orthopsychiatric Levy, J. The origins of lateral asymmetry. In S. Harnard, Association, New York, 1946. R. W. Doty, L. Goldstein, J. Jaynes & G. Krauthamer Bryden, M. P. Measuring handedness with question- (Eds.), Lateralization in the nervous system. Aca- naires. Neuropsychologia, 1977, 15, 617-624. demic Press, New York, 1977. Clark, M. M. Left-handedness: Laterality characteristics Levy, J., & Reid, M. Variations in cerebral organiza- and their educational implications. Univ. of London tion as a function of handedness, hand posture in Press, London, 1957. writing, and sex. Journal of Experimental Psychology: Collins, R. L. When left-handed mice live in right-handed General, 1978, 107, 119-144. worlds. Science, 1975, 187, 181-184. Morgan, M. S., & Corballis, M. C. On the biological Collins, R. L. Toward an admissible genetic model for basis of human laterality: II. The mechanisms of in- the inheritance of the degree and direction of asym- heritance. The Behavioral and Brain Science, 1978, metry. In S. Harnard, R. W. Doty, L. Goldstein, 2, 270-277. J. Jaynes, & G. Krauthamer (Eds.), Lateralization Porac, C, & Coren, S. Is eye dominance a part of gen- in the nervous system. Academic Press, New York, eralized laterality? Perceptual and Motor Skills, 1977. 1975, 40, 763-769. Corballis, M. C, & Morgan, M. H. On the biological basis Porac, C. & Coren, S. Individual and family patterns of human laterality: I. Evidence for a maturational in four dimensions of lateral preference. Neuro- left-right gradient. The Behavioral and Brain Sciences, psychologia, 1979, 17, 543-548. 1978,2. 261-269. Raczkowski, D., Kalat, J. W., & Nebes, R. Reliability Coren, S., & Porac, C. The validity and reliability of and validity of some handedness questionnaire items. self-report items for the measurement of lateral Neuropsychologia, 1974, 12, 43-48. preference. British Journal of Psychology, 1978, 69, Schulman-Galambos, C. Dichotic listening performance 207-211. in elementary and college students. Neuropsycho- Coren, S., Porac, C, & Duncan, P. A behaviorally logia, 1977, 15, 577-584. validated self-report inventory to assess four types Teng, E. L., Lee, P. H., Yang, K. S., & Chang, P. C. of lateral preference. Journal of Clinical Neuro- Handedness in a Chinese population: Biological, psychology, 1979, /, 55-65. social and pathological factors. Science, 1976, Dawson, J. L. M. An anthropological perspective on 193, 1148-1150. the evolution and lateralization of the brain. In S. J. Yakovlev, P., & Lecours, A. R. The myelogenetic cycle Diamond, & D. A. Blizard (Eds.), Evolution and of regional maturation of the brain. In A. Minkowski lateralization of the brain. New York Academy of (Ed.), Regional development of the brain in early Science, New York, 1977. life. David & Co., Philadelphia, 1967.

Downloaded from https://academic.oup.com/geronj/article-abstract/35/5/715/533241 by McGill University Libraries user on 05 November 2017