Fixed Effects Regression Methods for Longitudinal Data Using SAS

3.3. Estimation of Logistic Models for Two or More Observations Per Person

When individuals in the sample have three or more observations, we can't use the simple method of doing a logistic regression on the persons who change (with difference scores as predictors). In chapter 2, we faced the same problem with linear models, and we solved it by expressing all variables as deviations from the person-specific means. In the case of dichotomous outcomes, an analogous method can be implemented with PROC LOGISTIC (in SAS 9.0 and later).^[] Before proceeding to the practical details, I first need to clear up two theoretical issues: (1) the reason why we can't use dummy variables for individuals in logistic regression, and (2) the rationale for conditional ...