Within-Subjects Design

A within-subjects design refers to a study design where two or more measures are obtained from a sample of subjects. This type of design is also referred to as a repeated measures design. Three common circumstances lead to within-subjects designs. First, each subject is observed repeatedly in different conditions and the same measure is used as the outcome variable across the conditions. A main goal is to compare mean differences of the outcome variable across the conditions. Second, several related outcomes are measured collectively from each subject, such as an instrument with sub-scales, or related behavioral measures. Profile analysis is often conducted to evaluate the mean profile of subjects' scores across measures. Third, subjects' behaviors are measured at multiple occasions over time to study phenomena ...