Is It Random or Repeated?
Last week, a student in my Mixed Models Analysis Using SAS class sent in the following text message during a discussion of crossover designs (sometimes known as ABBA designs, where factors vary within subjects, not ABBA designs where you’re like a Super Trouper).
Does it make sense to look at repeated measures (multiple treatments) in the same way as repeated measures (over time)? Is the model essentially the same?
This is a common point of confusion for people learning mixed models, particularly if they have experience with other types of repeated measures analysis. It is also such a good question, one that is central to selecting a covariance structure in a mixed models analysis, that I decided to make a blog post of it.