Categorical Data Analysis Using The SAS® System, 2nd Edition

14.1. Introduction

Many types of studies have research designs that involve multiple measurements of a response variable. Longitudinal studies, in which repeated measures are obtained over time from each subject, are one important and commonly used type of repeated measures study. In other applications, the response from each experimental unit is measured under multiple conditions rather than at multiple time points. In some settings in which repeated measures data are obtained, the independent experimental units are not individual subjects. For example, in a toxicological study the experimental units might be litters; responses are then obtained from the multiple newborns in each litter. In a genetic study, experimental units might be defined ...