Basic Analysis and Graphing - SAS

60 Performing Univariate Analysis Chapter 2
Fit Distributions
Table 2.17 Descriptions of Plot Formats (Continued)
Plot Format
Applicable Distributions
The fitted probability versus the standard normal quantile • Johnson Sl
• Johnson Sb
• Johnson Su
• Glog
Table 2.18 describes the options in the red triangle menu next to Diagnostic Plot.
Table 2.18 Descriptions of the Diagnostic Plot Options
Rotate
Confidence
Limits
Line of Fit
Median
Reference
Line
Reverses the x- and y-axes.
Draws Lilliefors 95% confidence limits for the Normal Quantile plot, and 95% equal
precision bands with a = 0.001 and b = 0.99 for all other quantile plots (Meeker and
Escobar (1998)).
Draws the straight diagonal reference line. If a variable fits the selected distribution, the
values fall approximately on the reference line.
Draws a horizontal line at the median of the response.
Goodness of Fit
The Goodness of Fit option computes the goodness of fit test for the fitted distribution. The goodness of
fit tests are not Chi-square tests, but are EDF (Empirical Distribution Function) tests. EDF tests offer
advantages over the Chi-square tests, including improved power and invariance with respect to histogram
midpoints.
• For Normal distributions, the Shapiro-Wilk test for normality is reported when the sample size is less
than or equal to 2000, and the KSL test is computed for samples that are greater than 2000.
• For discrete distributions (such as Poisson distributions) that have sample sizes less than or equal to 30,
the Goodness of Fit test is formed using two one-sided exact Kolmogorov tests combined to form a near
exact test. For details, see Conover 1972. For sample sizes greater than 30, a Pearson Chi-squared
goodness of fit test is performed.
Related Information
• “Statistical Details for Fit Distribution Options” on page 84