# Normality of residuals in a regression model with a categorical IV

I have ran a simple regression with a continuous response variable and a categorical explanatory variable (with 2 levels). I am currently checking that the model meets the assumptions of regression. I produced the following plot:

I'm aware that I need to check that the residuals are normally distributed. Do I need to check the distribution of residuals at each of the 2 levels of the explanatory variable? Or do I need to check the distribution of all residuals simultaneously?

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@gung, you don't need homogeneity of variance to do a two sample $t$-test, do you? –  Macro Jul 21 '12 at 16:20