Development of Smoking by Birth Cohort in the Tob Control: First Published As 10.1136/Tc.8.2.161 on 1 June 1999
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Tobacco Control 1999;8:161–168 161 Development of smoking by birth cohort in the Tob Control: first published as 10.1136/tc.8.2.161 on 1 June 1999. Downloaded from adult population in eastern Finland 1972–97 Mikko Laaksonen, Antti Uutela, Erkki Vartiainen, Pekka Jousilahti, Satu Helakorpi, Pekka Puska Abstract whom only one in 10 smoked. Since then the Objective—To analyse the dynamics of prevalence of smoking has decreased notably smoking prevalence, initiation, and cessa- among men but among women it has almost tion in relation to sex, age, birth cohort, doubled. Among men the decrease has been study year, and educational level. similar in all age groups, whereas among Design—Six independent cross-sectional women the increase has been greatest in the population surveys repeated every five youngest age group.4 years between 1972 and 1997. One of the most important determinants of Setting—The provinces of North Karelia smoking behaviour is educational level. In and Kuopio in eastern Finland. eastern Finland less highly educated men have Subjects—Independent random samples been more likely to smoke than the more highly of 18 088 men and 19 200 women aged educated, and male smoking has decreased 25–64 years. Those comprising the oldest comparably across all educational categories. birth cohort were born in 1913–17 and Among women the more highly educated used those in the youngest were born in to smoke more than the less highly educated 1968–72. until the 1970s, after which the less highly edu- Results—Among men the prevalence of cated have been smoking more.5 smoking decreased over time, but the Birth cohort analysis may be used to gain cohort eVect observed in smoking further information on the development of initiation was obscured by the changes in smoking in the population. The aim of the smoking cessation. DiVerences between present study is to examine the dynamics of the educational categories were small. smoking in eastern Finland in relation to birth Among women the prevalence of smoking cohort, calendar year, and age during the http://tobaccocontrol.bmj.com/ increased during the study period. This period 1972–97. We used all three variables in was mainly caused by the less highly edu- our analyses but did not try to quantify their cated, in whom smoking initiation clearly separate eVects, because of their interaction. As increased in successive birth cohorts, but the changes in smoking prevalence result either a more moderate cohort eVect was also from initiation in successive birth cohorts or present among the more highly educated from changes in cessation within the birth women. cohorts, we analysed these components Conclusions—In men decreased initiation separately. The analyses were done separately and increased cessation contributed to the for men and women, and performed in two downward trend in smoking prevalence, educational categories. whereas among women, changes in smok- ing were mostly caused by augmented ini- on September 30, 2021 by guest. Protected copyright. tiation in successive birth cohorts. During Methods the study period educational inequalities The data were derived from six cross-sectional in smoking widened, as the less highly risk factor surveys conducted in eastern educated came increasingly to form the Finland since 1972. Independent population smoking population. samples were studied every five years in the National Public Health provinces of North Karelia and Kuopio. In Institute, Department (Tobacco Control 1999;8:161–168) 1972 and 1977 random samples of 6.6% of the of Epidemiology and Keywords: smoking prevalence; smoking initiation; Health Promotion, smoking cessation; Finland population born between 1913 and 1947 were Helsinki, Finland drawn in both provinces. In 1977 an additional M Laaksonen A Uutela sample of 6.6% of those born between 1948 E Vartiainen Introduction and 1952 was taken randomly in North Kare- P Jousilahti The health hazards of smoking have been well lia only. For the subsequent surveys (1982, S Helakorpi P Puska established. Smoking is one of the most impor- 1987, 1992, and 1997) the sampling method tant risk factors for cardiovascular disease was modified to comply with the protocol of Correspondence to: (CVD) and also increases the risk for dozens of the World Health Organisation MONICA M Laaksonen, National 12 Public Health Institute, other diseases. During the early 1970s project (monitoring trends and determinants in Department of Epidemiology eastern Finland was reported to have the high- cardiovascular disease).6 The sample was and Health Promotion, Mannerheimintie 166, est mortality from CVD in the world. High lev- stratified according to sex and 10-year age FIN-00300 Helsinki, els of the main CVD risk factors, smoking group so that at least 250 people were included Finland; Mikko.Laaksonen@ktl.fi among them, have been reported to be in each subgroup in both provinces. Because in contributing factors to this.3 the earliest surveys the population aged 25–64 24 April 1998 and in revised form 23 July 1998. Accepted Thirty years ago half the men in eastern Fin- years was equally distributed to each 10-year 23 August 1998. land smoked, in contrast to women, among age group, the results remained comparable. 162 Laaksonen, Uutela, Vartiainen, et al Our analyses included 25–64 year olds, except socioeconomic status, educational level is the Tob Control: first published as 10.1136/tc.8.2.161 on 1 June 1999. Downloaded from in 1972 when 60–64 year olds were not one showing the strongest and most consistent studied. In 1977 the age group 25–29 years old associations with CVD risk factors.78 Here, consisted of North Karelians only. The educational level was measured by the total number of respondents in the six surveys was number of school years. As the average length 37 288, and the response rates varied between of education in Finland has increased remark- 75% and 92%. ably during the recent decades, the As the overall development of smoking in the respondents were divided into two educational two provinces has been basically similar, categories on the basis of their position below despite the somewhat steeper decrease in male or above the median length of education in smoking in North Karelia during the first their own birth cohort. surveys,4 the data from the two areas were The results are presented in the tables, combined for our analyses. Twelve synthetic stratified by sex and educational level, using five-year birth cohorts were constructed; those five-year birth cohorts, five-year study periods included in the oldest birth cohort were born and five-year age groups as classifying in 1913–17 and those in the youngest cohort variables. Birth cohorts appear in rows and were born in 1968–72. The number of study years in columns, and trends at each age respondents decreased progressively from the level can be traced by reading diagonally down earliest to later surveys. The smallest cell and to the right. Even if the results do not allow defined by birth cohort, age, study year, and complete separation of age, period, and birth sex included 135 respondents. cohort from each other, simultaneous use of Respondents’ smoking status was assessed the three variables can produce tentative with standardised questions in a self evidence about their relative contribution to administered questionnaire. Those who had the development of smoking. smoked regularly for at least one year and con- Logistic regression analysis was used to test tinued to do so during the previous month the statistical significance between the were regarded as current smokers. Smoking explanatory factors and the smoking variables. initiation was defined on the basis of ever hav- The order of the modelling follows the order in ing smoked regularly; those who declared they the text. The models birth cohort, age group, had smoked for at least one year at some point and study year were treated as continuous vari- during their lifetime were considered as smok- ables. First-level interactions between the main ing initiators. Quitters were those who had eVects were also tested. Odds ratios with smoked regularly but stopped at least one significance levels for five-year increase in age, month before the study. five-year period, five-year diVerence in birth The analyses were performed in two educa- cohort, and change from lower to higher http://tobaccocontrol.bmj.com/ tional categories. Among the indicators of educational level are shown in the table Table 1 Current smoking by birth cohort, age (in diagonals), study year, and educational level in men Current smokers by year (%) Birth cohort 1972 1977 1982 1987 1992 1997 Age (years) Less highly educated men 1913–1917 52 39 1918–1922 57 42 38 1923–1927 55 48 36 31 1928–1932 54 48 34 34 23 1933–1937 53 44 43 35 34 24 1938–1942 54 44 35 40 33 29 60–64 on September 30, 2021 by guest. Protected copyright. 1943–1947 53 53 46 40 43 31 55–59 1948–1952 52 49 49 32 42 50–54 1953–1957 53 50 42 37 45–49 1958–1962 48 43 39 40–44 1963–1967 42 42 35–39 1968–1972 48 30–34 25–29 Total 54 46 42 40 36 35 More highly educated men 1913–1917 48 28 1918–1922 49 45 37 1923–1927 53 38 30 26 1928–1932 46 40 38 34 23 1933–1937 37 38 42 26 24 23 1938–1942 45 41 34 31 28 19 60–64 1943–1947 55 42 33 32 33 29 55–59 1948–1952 46 40 41 35 32 50–54 1953–1957 39 33 37 34 45–49 1958–1962 27 31 29 40–44 1963–1967 29 13 35–39 1968–1972 37 30–34 25–29 Total 48 40 37 32 31 27 Odds ratios and significance levels from logistic regression analyses: one-factor models: study year 0.85 (p<0.001); age group 0.93 (p<0.001); birth cohort 0.99 (p = 0.15); education 0.78 (p<0.001).