A SAS program for evaluating person-years of risk in cohort studies

A SAS macro, written to evaluate person-years of exposure in longitudinal studies, is presented in this paper. The program has the advantage of stratification by age groups and chronological subperiods, a feature recommended in long-term studies, involving temporal changes in patterns of outcome. The program creates a data set that can be utilized to calculate age-adjusted incidence rates in categories of risk factors for morbidity and mortality.