Iurie,
Noel, thanks a lot. This will help me someday. But I have a question.
When we run Shapiro-Wilk test, the homogenity of variances is a
mandatory condition?
No it is not. An homoscedasticity test only makes sense when you have a
grouping factor, and a normality test may of course be used in a variety
of contexts when you have a unique sample.
My point was: If you use gaussian models and assume homogeneity of
within-group variances, then testing normality is somewhat simplified,
since your model residuals are expected to be drawn from a unique normal
distribution, and only one normality test on the residuals is necessary
(no need for a loop).
Best wishes,
Yvonnick NOEL, PhD.
University of Brittany, Rennes 2
France
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