Prior to conducting a 2 (between-group factor: 2 levels) by 2 (within-group factor: 2 levels) mixed ANOVA in R, I would like to test whether the residuals of my outcome variable are normally distributed. This is one of the assumptions of the mixed ANOVA.
My question is: How can I obtain the (studentized) residuals of my outcome variable in R?
Help is very much appreciated. Thank you!