Repeated surveys — a technique for asking the same questions to different samples of people — allows researchers the opportunity to analyze changes in society as a whole. This book begins with a discussion of the classic issue of how to separate cohort, period, and age effects. It then covers methods for modeling aggregate trends; two methods for estimating cohort replacement's contribution to aggregate trends, a decomposition model for clarifying how microchange contributes to aggregate change, and simple models that are useful for the assessment of changing individual-level effects.