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 modelling 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.