The Half Normal Plot shows the absolute value of the contrasts plotted against the absolute value of quantiles for the half-normal distribution. The blue line passes through the origin with a slope of the Lenth’s estimate of σ. Effects that are small are considered error terms and assumed to have a normal distribution with mean zero and standard deviation σ. These terms fall on the blue line. Significant effects are those that have nonzero means and do not fall on the blue line.
The Half Normal Plot is interactive. You can select model effects by dragging a rectangle around the effects of interest. You can also hold down the Ctrl button and click an effect name(s) in the report.