Currently I had analyzed normalcy using the goodness of fit by Shapiro-Wilk test for Y variable at each time point. In my case, the distribution is not normal (p is significant in the Shapiro-Wilk test). In a situation where even at a one-time point (among the 3-time points) the distribution is abnormal, I am presuming to apply a nonparametric test.
Not sure if this is the right way of looking at the normalcy or evaluating the differences in cases and controls over the 3-time points. Please suggest.