# QQ plot is consistent with normality when subgroups are non-normal

I have read that for a one way ANOVA, you should check that the model residuals are normally distributed. If the variance of each group is homogeneous then this implies that the residuals with each group being compared are also normally distributed

So let's say we are doing an ANOVA to compare the means for two groups. Data for each group resembles a skewed distribution and both have approximately equal variance but one group is positively skewed, and a the other is negatively skewed. A histogram or QQ plot of model residuals would probably indicate normality of residuals, and therefore normality of each group. However this is clearly not the case. So my question is what am I missing?

• Good edits to both your question and my answer, thanks. – Glen_b -Reinstate Monica Mar 16 '13 at 5:24