
Hello R and statistics experts,
(Sorry for this probably basic question. I know there is a lot written about this topic, but it is still not clear to me.)

My data has one between-subject factor ("group", 2 levels, n=10 per group) and one within-subject factor ("session", 2 levels). I would like to use the ezANOVA function to test for main effects and interactions. 


Now, how do I check whether the assumptions of equal variance and normality are fulfilled (which have to be fulfilled in order to use ezANOVA, right)?


As I understood, Mauchly’s test (which would give me an information about the equality of variances) is only calculated by ezANOVA if I have more than two within-subject levels.


Do I have to check the normality of the residuals for each of the 4 condition combinations with e.g. the following functions: qqnorm(mpg), qqline(mpg), shapiro.test(x)? How do I however get the residuals in order to do this? Then, should I use for example the Fligner-Killeen test for homogeneity of variances of all 4 condition combinations?

I would be grateful for any advice!
Thanks,Marianne 		 	   		  
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