I want to test the differences in my interval-scaled dependent variable - measured at three time intervals (within subj.), for two conditions (within subj.), while accounting for a interval-scaled covariate that has two values per subject (one per condition).
Sample size is low twenties. Data looks like this:
To my understanding, a typical repeated measures ANOVA struggles with this because the covariate has different values for the same person depending on the second within subject factor. I was wondering if a mixed model could accommodate the design, but my knowledge of lme4 is too limited.
Could someone share an insight?