The SEVERITY procedure was experimental in SAS/ETS 9.22. PROC SEVERITY is now production status. The following new features and updates have been added to the SEVERITY procedure:
The following updates have been made to the syntax:
The MODEL statement is now replaced with LOSS and SCALEMODEL statements. The LOSS statement specifies the response variable along with any censoring and truncation information. The SCALEMODEL statement specifies the regressor variables. The model-fitting options that were specified in the MODEL statement in SAS/ETS 9.22 should now be specified in the PROC SEVERITY statement.
You can now specify multiple distributions in one DIST statement. You can also use a keyword to specify a group of distributions. The syntax for specifying initial parameter values of a distribution has also been updated. If you do not specify a DIST statement, then PROC SEVERITY produces only the empirical CDF estimates and does not fit all predefined distributions by default.
You can specify the number of occurrences for each observation by using the new FREQ statement.
You can specify left-censoring and right-truncation by using the new LEFTCENSORED= and RIGHTTRUNCATED= options in the LOSS statement.
The method of specifying censoring has been updated. Instead of using the indicator variable, you now specify censoring by using a variable that contains the censoring limit. This enables you to specify interval-censored data; that is, data in which observations are both right-censored and left-censored.
For interval-censored data, PROC SEVERITY uses Turnbull’s method to estimate the empirical distribution function (EDF). Implementation of Turnbull’s EDF estimation method is an experimental feature in SAS/ETS 9.3.
Two predefined versions of Tweedie distributions, TWEEDIE and STWEEDIE, can be fitted with PROC SEVERITY. The TWEEDIE distribution has the more popular parameterization with mean, dispersion, and index parameters. The STWEEDIE distribution has an alternative parameterization with scale, Poisson mean, and index parameters. The STWEEDIE distribution can be used for analyzing regression effects.
You can estimate parameters by minimizing your own objective function, which can be specified using SAS programming statements. You can use various keyword functions in your SAS program, which are internally expanded by PROC SEVERITY with distribution-specific or problem-specific versions.
This is an experimental feature in SAS/ETS 9.3.
You can now compute quantile and limited moment for any distribution fitted with PROC SEVERITY by using the two new functions, INVCDF and LIMMOMENT, respectively. These functions are accessible in a PROC FCMP step.