I have a study with 35 subjects who received hypercoagulability testing at 4 different times (before surgery, after, at 1 week, and at 1 month). Each subject has 9 different test of hyper coagulability at the 4 time points. I want to compare each of these 9 tests over time (i.e.: clot time_preop vs. clot time_postop vs. clot time_1wk vs clot time_1mo) to see if they change.
One issue I am having is how to decide if my data is normal. How do I assess for normality in the data? I have explored the data in SPSS and see that although most are normal, some are not. If one of the measurements in a variable (i.e.: clot time_1wk) is not normal (kurtosis=10 and Shapiro-Wilk <0.01) but the others are, should I use Friedman non-parametric instead? Or should I be assessing normality another way?