This lesson introduced us to the topic of repeated measures designs. The focus was on repeated measures in time where each experimental unit is assigned to exactly one treatment level the response is observed over several time periods. The responses from the same experimental unit observed over time can be correlated and the model assumption of independent observations is no longer valid. Therefore, an appropriate covariance structure should be imposed to account for the correlated nature of the response, and the best is chosen based on fit statistics. 

Other scenarios can result in repeated measures, not necessarily over time. In a repeated measure design, the important feature is that multiple measurements are being made on the same experimental unit. Another case of this is the cross-over design wherein the treatments themselves are switched on the same experimental unit during the course of the experiment. This will be the topic of the next lesson.