Printed in U.S.A. DOI: 10.1093/aje/kwg011 Birth Cohort Effect on Prevalence of Age-related Maculopathy in the Beaver Dam Eye

The number of people in the United States with age-related maculopathy is increasing in recent years because of increasing longevity. However, it is possible that a birth cohort effect, due to different levels of exposure to risk factors, may explain changes in the prevalence of age-related maculopathy by age. In this report, the authors utilize data from the population-based Beaver Dam Eye Study (1988–2000) to examine this possibility. They propose a strategy to handle issues of longitudinal measurements and risk factor adjustment for analyzing the birth cohort effect. Results from the analysis (after adjusting for known risk factors) showed an apparent independent birth cohort effect on age-related maculopathy. The authors also found a strong positive association between age-related maculopathy and age, when comparing participants from the same birth cohort. The birth cohort effect was the same across different age groups, except for early age-related maculopathy, where older age increased the association. Our findings demonstrate that the birth cohort effect is likely attributable to unmeasured risk factors for age-related maculopathy and limitations of risk factor measurements. Further study of possible unmeasured risk factors that cause the cohort effect may help us understand the etiology of the disease. cohort effect; cohort studies; generalized estimating equation; macular degeneration; risk adjustment Abbreviations: CI, confidence interval; OR, odds ratio