Repeated measures

Repeated measures designs contain several measurements for the same experimental unit. This generally occurs when we assign different doses of a treatment to a unit and want to evaluate the response through time.

We now have a fixed effect for time, which is typically coded as 1,2,3..,k that needs to be added. We would expect that this variable/effect will have an impact on the response.

These designs raise four major points, and we need to decide how to solve them:

• Do we think that time has the same impact for all of the experimental units? We have two options for this:
  • If yes, we will just add the time variable as a fixed effect.
  • If no, we will still add the time variable as a fixed effect, plus a random effect for time by subject. What this means is that the time effect can be obtained as the sum of the fixed effect (average for all units) plus the random...