2.3. Extending the Model
The model of equation (2.2) is somewhat restrictive because it assumes that the regression slopes are invariant across time. This assumption can be tested and relaxed. Consider the model
which is identical to equation (2.2) except that the β coefficient is allowed to differ for times 1 and 2. The difference score equation then becomes
which, with a little algebra, can also be written as
This equation says that both ( ...
Get Fixed Effects Regression Methods for Longitudinal Data Using SAS now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
