I have a repeated measures design (one DV measured twice, both times in two different conditions) with one continuous IV and one (continuous) covariate. I'm trying to see if there is an interaction between the IV and the within-subject variables while controlling for the covariate. ANOVA family techniques will not work because I don't want to dichotomize the IV.
Is a mixed-effects model with crossed random effects the best way to analyze the data? Can the model include two within-subject variables? Or is it better to have two separate mixed-effects models with one within-subject variable each? Sample size is over 120. I'm new to mixed-effects model, so any insights and comments would be helpful! Thank you!