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

If a QQ plot is requested (with a PLOT statement of the form PLOT yvariable*NQQ.), the ithordered value is represented by a point with ycoordinate and xcoordinate , where is the standard normal distribution.
If a PP plot is requested (with a PLOT statement of the form PLOT yvariable*NPP.), the ithordered value is represented by a point with ycoordinate and xcoordinate , where is the mean of the nonmissing xvalues and is the standard deviation. If an xvalue has multiplicity k (that is, ), then only the point is displayed.