While epidemiologic surveys in the U.S. have consistently found higher lifetime prevalence of alcohol dependence among younger subjects than among older groups, these results have generally been interpreted cautiously because such analyses necessarily compare retrospectively reported behaviors among different birth cohorts reporting from vastly different ages. In this report, we control for the influence of age-related factors by comparing subgroups of subjects from two different surveys, conducted ten years apart, categorically matched on the basis of age and other demographic factors. This approach allowed different birth cohorts to be compared at the same age. Among women, significant increases in the lifetime prevalence of drinking were observed for the 1944–53 birth cohort, compared to their immediate predecessor (1934–43, see 48–57 year old comparisons, ). There was a further increase in the lifetime prevalence of drinking and, among drinkers, there was an increase in lifetime prevalence of alcohol dependence for the following birth cohort (1954–1963; see 38–47 year old comparisons). Hence, after controlling for age-related factors, secular changes in alcohol dependence for women remain significant. Among men, however, only a few, marginally significant differences in drinking or alcohol dependence were observed when temporally adjacent birth cohorts were compared, suggesting that these outcomes have remained fairly constant across the birth cohorts of men sampled in these surveys.
The findings in women and patterns by race/ethnicity can be summarized as follows: an increase in risk for drinking and alcohol dependence among drinkers has apparently taken place beginning with the first cohorts born after World-War II, with no reduction to earlier baseline levels observed for more recent birth cohorts. The changes seem to have affected White and Hispanic women, but not Black women. We also note a marginally significant, but potentially substantial increase in alcohol dependence for Hispanic women born between 1974 and 1983, the most recent birth cohort sampled in the two surveys, compared to their predecessors. While caution is in order due to low statistical power for this comparison, further monitoring of trends in this demographic group are clearly in order. Likewise, elevated rates of drinking were seen in the youngest cohort of Black women, compared to their predecessors.
These findings extend the current literature in several ways. First, by taking an analytical approach that has not been previously applied to secular analyses of alcohol dependence, we have shown that secular increases in lifetime alcohol dependence for women remain significant after adjusting for age-related effects, but that few secular changes among men are apparent after accounting for age-related effects. These findings confirm previous reports that have suggested a narrowing of the gender gap in alcohol dependence (Greenfield et al., 2003
; Holdcraft and Iacono, 2002
) while showing that the increase among women is observed primarily among Whites and Hispanics. Additionally, we have shown that the secular trends suggested by analyses of single cross-sectional epidemiological surveys are likely to be confounded by age-related factors, such that the increase in risk for more recently born cohorts has been overestimated. This finding underscores the importance of controlling for such effects as has been done here.
Inverse Association Between Age and Lifetime Prevalence of Alcohol Dependence
The importance of considering age-related factors when estimating secular trends is demonstrated by the cross-survey comparisons of subjects from the same birth cohorts, who, by design, have different age ranges in the two surveys. Cohorts in the NESARC consistently reported 9–14% lower prevalence of lifetime alcohol dependence than equivalent birth cohorts in the earlier NLAES. Because lifetime alcohol dependence is a cumulative diagnosis, and we controlled for population change by limiting analyses to U.S. born subjects, the major contributors to decreased lifetime prevalence of alcohol dependence within a cohort over time are expected to be differential mortality and age-dependent measurement error. Differential mortality is likely to play a role in the within-cohort reduction in lifetime prevalence of alcohol dependence between surveys, but is unlikely to account for the majority of the change. The estimated number of U.S. deaths attributable to excessive alcohol use in 2001 was 75,000 or 0.025% of the population (Midanik et al., 2004
). This corresponds to about 0.25% of the population over ten years. According to , the population reports 12% fewer cases of alcohol dependence after aging ten years; the number of cases lost corresponds to 2.1% of the total population. Hence, even under a “worst case” assumption in which alcohol-related mortality effects cases only, differential mortality can account for only a minor proportion of the total reduction in reported cases.
Although the results presented here cannot be used to determine the specific reasons that cohort prevalence declines with age, systematic measurement error, such as recall or response bias, is one likely source. Such measurement error could reflect a number of factors. Older subjects may under-report remitted symptoms due to recall problems or response bias and may, in general, have a different perspective on symptom reporting. Also, as suggested elsewhere, younger subjects may misinterpret survey questions so as to report consequences of occasional heavy drinking episodes as symptoms of alcohol dependence. Hence, over-reporting of alcohol dependence symptoms among younger subjects is also a possibility (Caetano and Babor, 2006
Increase in Alcohol Dependence Risk for Women
Altogether, these data suggest that there has been a substantial change in the demographic distribution of drinking and alcohol dependence. The increase in prevalence among White and Hispanic women contributes to a substantial narrowing in the gap between male and female alcohol dependence. These findings have important implications for physicians because female alcoholics are under-identified in primary care settings, with under-identification in older women being especially problematic (CASA), 1998
; Brienza and Stein, 2002
; Green, 2006
). Furthermore, women perceive more stigmatization and face greater barriers to treatment than men with alcohol dependence, and may be under-represented in specialized treatment settings (Brady and Ashley, 2005
; Green, 2006
.; Thom, 1987
) This is particularly disturbing because women with alcohol problems face more severe health-related consequences and possibly more years of life lost than their male counterparts (Bradley et al., 1998
; Jarque-Lopez et al., 2001
; Smith et al., 1994
). In addition to improved treatment access, primary prevention efforts directed toward young women are also needed.
Why have lifetime drinking and alcohol dependence prevalence in women become closer to those for men? It may be that through entry into the work force and other steps toward gender equity, cultural and economic conditions for women born after World War II in the U.S. more closely resemble those of men. Indeed, such factors have been invoked to explain the narrowing gender gap found in other studies (Holdcraft and Iacono, 2002
). Identification of specific environmental factors responsible for these changes is of interest for the rational design of prevention strategies. Among the myriad candidates are greater economic power for women, facilitating purchasing power for alcohol, (Becker and Murphy, 1999
), the correlation between drinking behavior and occupational subcultures (Ames and Rebhun, 1996
), and changes in women’s attitudes toward alcohol in the post-prohibition era (Murdock, 1998
). As a result of potentially numerous social and cultural changes, the stigma associated with drinking behavior among women may have been reduced in recent years. Unfortunately, a corresponding reduction in barriers to alcoholism treatment has apparently not been realized.
Although this report extends the existing literature in several ways, there are a number of limitations to these results. One such limitation is that the two surveys analyzed used similar methods; while this is necessary for the types of analyses conducted here, it also means that any method-specific biases will be common to both surveys. Ideally, these findings should be replicated with data collected using a variety of methods. In addition, we were not able to examine minority groups other than from Blacks and Hispanics, due to low statistical power for stratified groups. Finally, the exclusion of older subjects due to mortality concerns, and the unavailability of data on younger subjects limits the window of birth years that could be analyzed here, making it difficult to interpret our findings in a broader historical context.
National epidemiological surveys in the U.S. have consistently shown an inverse association between age and the lifetime prevalence of alcohol dependence, but whether such trends are confounded by age-related recall or response effects has been unclear. By comparing temporally adjacent birth cohorts from two such surveys, while controlling for age and other demographic factors through category-matching, we have shown that important differences between birth cohorts remain after matching for age, but that such differences are limited to women. The largest change detected was that women born after 1953 were at higher risk for drinking, and those who drank had higher risk for alcohol dependence, compared with earlier birth cohorts. These differences were observed among White and Hispanic women, but not Black women. Analyses of single cross-sectional studies may tend to over-estimate secular trends by failing to account for such age-dependent effects.