Normality

In the next example, we see QQ plots where the residuals deviate from the diagonal line in both the upper and lower tail. The left hand side plot indicates that the tails are ‘lighter’ (have smaller values) than what we would expect under the standard modeling assumptions. This is indicated by the points forming a “flatter” line than than the diagonal.

On the right hand side, we see a QQ plot where the residuals deviate from the diagonal line in both the upper and lower tail. Unlike the previous plot, in this case we see that the tails are observed to be ‘heavier’ (have larger values) than what we would expect under the standard modeling assumptions. This is indicated by the points forming a “steeper” line than the diagonal.