We conducted an experiment to determine if type of blood is a main effect or interact with a treatment (2 treatments). The subjects were measured on several hours (5 times). There are 3 subjects by type of blood (these are replicates). Then, we have the effects of TYPE, TREATMENT, TIME.
We are not sure if Time is a covariate, we think Time as a factor because we don't look for a specific behavior on Time, only at 5 Times, to have a replication in Time (then Time can be random factor). However, TYPE and TREATMENT are fixed factors.
This is a repeated measures design or mixed model, or simply ANOVA with 2 fixed and one random factor (within ¿?).
Thank you.
Best Answer
Don't forget the SUBJECT random effect. That's the one that makes it into a repeated measures/mixed model design. You are correct that TYPE and TREATMENT are fixed, but how to treat TIME will depend on what assumptions you want to make about time. The simplest thing to do would just be to leave it out and treat the five measures as independent subsamples on each individual, but more generally, you could treat TIME as a fixed effect/repeated measure and model the correlation between each time point.
The preferred terminology in these models can differ depending on your field; as the same model can often be described several ways, so it's not really a matter of deciding whether it's a repeated measure/mixed model/ANOVA; you could probably use any of those terms to describe the model you end up with. What's more important is to define what terms you want to include in the model and how you want them to be able to vary.