Base SAS 9.1.3 Procedures Guide - Acsu Buffalo

372 Chapter 3. The UNIVARIATE Procedure
Output 3.31.4. Lognormal Quantile-Quantile Plot (σ =est, ζ =est, θ =5)
From the plot in Output 3.31.2, σ can be estimated as 0.51, which is consistent with
the estimate of 0.5 derived from the plot in Output 3.31.2. The next example illustrates
how to estimate percentiles using lognormal Q-Q plots.
A sample program, uniex18.sas, for this example is available in the SAS Sample
Library for Base SAS software.
Example 3.32. Estimating Percentiles from Lognormal
Quantile Plots
This example, which is a continuation of the previous example, shows how to use a Q-
Q plot to estimate percentiles such as the 95th percentile of the lognormal distribution.
A probability plot can also be used for this purpose, as illustrated in Example 3.26.
The point pattern in Output 3.31.4 has a slope of approximately 0.39 and an intercept
of 5. The following statements reproduce this plot, adding a lognormal reference line
with this slope and intercept:
symbol v=plus;
title ’Lognormal Q-Q Plot for Diameters’;
proc univariate data=Measures noprint;
qqplot Diameter / lognormal(sigma=0.5 theta=5 slope=0.39 noprint)
pctlaxis(grid)
vref = 5.8 5.9 6.0
square;
run;
The result is shown in Output 3.32.1: