## Construction of Q-Q and P-P Plots

If a normal probability-probability or quantile-quantile plot for
the variable *x* is requested, the *n* nonmissing values of *x*
are first ordered from smallest to largest:

If a Q-Q plot is requested (with a PLOT statement of the
form PLOT *yvariable**NQQ.),
the *i*^{th} ordered value *x*_{(i)} is represented
by a point with *y*-coordinate *x*_{(i)} and *x*-coordinate
,where is the standard normal distribution.
If a P-P plot is requested (with a PLOT statement of the
form PLOT *yvariable**NPP.),
the *i*^{th} ordered value *x*_{(i)} is represented
by a point with *y*-coordinate [*i*/*n*] and
*x*-coordinate ,where is the mean of the nonmissing *x*-values and is
the standard deviation. If an *x*-value has multiplicity *k* (that is,
*x*_{(i)} = ... = *x*_{(i+k-1)}), then only the
point is displayed.

Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.