I have just conducted an experiment in which I have measured glucose concentration in patients (4 different treatment groups) at 3 different weeks ( pre, 6 weeks and 12 weeks). I want to use Mixed Anova to test if there is any significant difference between treatments in glucose concentration (also possible time and time*treatment interaction).
However, Mixed Anova requires the data to be normally distributed. I am using SPSS. Must I perform for example a Kolmogorov‐Smirnov/Shapiro-Wilks test (glucose data (group1, time1,...,etc.) of every group separately (at each time point)? Or is there another way to look at normality before running Mixed Anova?