The UNIVARIATE Procedure
Estimating Shape Parameters Using Q-Q Plots
Some of the distribution options in the PROBPLOT or QQPLOT statements require you to specify one or two shape parameters in parentheses after the distribution keyword. These are summarized in Table 34.
You can visually estimate the value of a shape parameter by specifying a list of values for the shape parameter option. A separate plot is produced for each value, and you can then select the value of the shape parameter that produces the most nearly linear point pattern. Alternatively, you can request that the plot be created using an estimated shape parameter. See the entries for the distribution options in the section Dictionary of Options (for the PROBPLOT statement) and in the section Dictionary of Options (for the QQPLOT statement).
Note: For Q-Q plots created with the WEIBULL2 option, you can estimate the shape parameter c from a linear pattern by using the fact that the slope of the pattern is 
.
Table 34: Shape Parameter Options
| Distribution Keyword | Mandatory Shape Parameter Option | Range |
|---|---|---|
| BETA | ALPHA= , BETA= |  ,  |
| EXPONENTIAL | None | |
| GAMMA | ALPHA= | |
| GUMBEL | None | |
| LOGNORMAL | SIGMA= |  |
| NORMAL | None | |
| PARETO | ALPHA= | |
| POWER | ALPHA= | |
| RAYLEIGH | None | |
| WEIBULL | C=c |  |
| WEIBULL2 | None |