The REG Procedure

Construction of Q-Q and P-P Plots

If a normal probability-probability or quantile-quantile plot for the variable $\text{[math]}$ is requested, the $\text{[math]}$ nonmissing values of $\text{[math]}$ are first ordered from smallest to largest:

$\text{[math]}$

If a Q-Q plot is requested (with a PLOT statement of the form PLOT yvariable $\text{[math]}$ NQQ.), the $\text{[math]}$ th-ordered value $\text{[math]}$ is represented by a point with y-coordinate $\text{[math]}$ and x-coordinate $\text{[math]}$ , where $\text{[math]}$ is the standard normal distribution.

If a P-P plot is requested (with a PLOT statement of the form PLOT yvariable $\text{[math]}$ NPP.), the $\text{[math]}$ th-ordered value $\text{[math]}$ is represented by a point with y-coordinate $\text{[math]}$ and x-coordinate $\text{[math]}$ , where $\text{[math]}$ is the mean of the nonmissing $\text{[math]}$ -values and $\text{[math]}$ is the standard deviation. If an $\text{[math]}$ -value has multiplicity $\text{[math]}$ (that is, $\text{[math]}$ ), then only the point $\text{[math]}$ is displayed.