Testing Normality for Levels

Hi. So first, I ran the code:

if(!require("MASS")) install.packages("MASS")

which gives me a built-in data in R Studio called 'crabs'.

Assuming that variance is homogeneous, I was asked to draw a QQ plot to test for normality. However, since the normality here means the ERROR's normality, it says that I should not draw a QQ plot for the whole data but instead draw for each group in the sp and sex variables (total 4 groups: sp O and sp B, sex F and sex M) and test for each of their normality. However, the both variables are in the 'levels' form (levels: B O and levels: M F) and they are not numbers either.
How will I be able to do these normality (qq plot) tests?

Thank you!

This topic was automatically closed 21 days after the last reply. New replies are no longer allowed.