Categorized Plots, 2D - Half-Normal Probability Plots

normal probability plot is constructed in the same manner as the standard normal probability plot , except that only the positive half of the normal curve is considered. Consequently, only positive normal values will be plotted on the Y-axis. This plot is often used in plots of residuals (e.g., in multiple regression), when one wants to ignore the sign of the residuals, that is, when one is interested in the distribution of absolute residuals, regardless of the sign.
For a detailed discussion of Categorized Graphs, see Categorized Graphsin Selected Topics in Graphical Analytic Techniques .