I am working on an RCT measuring change in scores from baseline; Total N = 60 with 3 arms (1:1:1, no dropouts). I was going for ANCOVA comparing the follow up values between the 3 groups while adjusting for baseline ones.

However, the variances are quite heterogeneous, and outliers exist. I am not sure if the model would be robust in this scenario. I thought of rank transformation, but is there a better alternative? Perhaps a “non-parametric” ANCOVA or another suitable linear model?

I appreciate your input!