The SEVERITY Procedure

CLASS Statement

CLASS variable <(options)> …<variable <(options)>> </ global-options>;

The CLASS statement names the classification variables to be used in the scale regression model. These variables enter the analysis not through their values, but through levels to which the unique values are mapped. For more information about these mappings, see the section Levelization of Classification Variables.

If you specify a CLASS statement, then it must precede the SCALEMODEL statement.

You can specify options either as individual variable options or as global-options. You can specify options for each variable by enclosing the options in parentheses after the variable name. You can also specify global-options for the CLASS statement by placing them after a slash (/). Global-options are applied to all the variables that you specify in the CLASS statement. If you specify more than one CLASS statement, the global-options that are specified in any one CLASS statement apply to all CLASS statements. However, individual CLASS variable options override the global-options.

You can specify the following values for either an option or a global-option:

DESCENDING DESC

reverses the sort order of the classification variable. If you specify both the DESCENDING and ORDER= options, the SEVERITY procedure orders the levels of classification variables according to the ORDER= option and then reverses that order.

specifies the sort order for the levels of classification variables. This order is used by the parameterization method to create the parameters in the model. By default, ORDER=FORMATTED. For ORDER=FORMATTED and ORDER=INTERNAL, the sort order is machine-dependent. When ORDER=FORMATTED is in effect for numeric variables for which you have supplied no explicit format, the levels are ordered by their internal values.

The following table shows how the SEVERITY procedure interprets values of the ORDER= option.

Value of ORDER=	Levels Sorted By
DATA	Order of appearance in the input data set
FORMATTED	External formatted values, except for numeric variables that have no explicit format, which are sorted by their unformatted (internal) values
FREQ	Descending frequency count (levels that have more observations come earlier in the order)
FREQDATA	Order of descending frequency count, and within counts by order of appearance in the input data set when counts are tied
FREQFORMATTED	Order of descending frequency count, and within counts by formatted value when counts are tied
FREQINTERNAL	Order of descending frequency count, and within counts by unformatted (internal) value when counts are tied
INTERNAL	Unformatted value

For more information about sort order, see the chapter about the SORT procedure in Base SAS Procedures Guide and the discussion of BY-group processing in SAS Language Reference: Concepts.

REF=’level’ | keyword REFERENCE=’level’ | keyword

specifies the reference level that is used when you specify PARAM= REFERENCE. For an individual (but not a global) variable REF= option, you can specify the level of the variable to use as the reference level. Specify the formatted value of the variable if a format is assigned. For a REF= option or global-option, you can use one of the following keywords.

FIRST: designates the first-ordered level as reference.
LAST: designates the last-ordered level as reference.

By default, REF=LAST.

If you choose a reference level for any CLASS variable, all variables are parameterized in the reference parameterization for computational efficiency. In other words, the SEVERITY procedure applies a single parameterization method to all classification variables.

Suppose that the variable temp has three levels (hot, warm, and cold) and that the variable gender has two levels (M and F). The following statements fit a scale regression model:

proc severity;
   loss y;
   class gender(ref='F') temp;
   scalemodel gender*temp gender;
run;

Both CLASS variables are in reference parameterization in this model. The reference levels are F for the variable gender and warm for the variable temp, because the statements are equivalent to the following statements:

proc severity;
   loss y;
   class gender(ref='F') temp(ref=last);
   scalemodel gender*temp gender;
run;

You can specify the following global-options:

MISSING

treats missing values (".", ".A", …, ".Z" for numeric variables and blanks for character variables) as valid values for the CLASS variable.

If you do not specify the MISSING option, observations that have missing values for CLASS variables are removed from the analysis, even if the CLASS variables are not used in the model formulation.

PARAM=keyword

specifies the parameterization method for the classification variable or variables. You can specify the following keywords:

GLM: specifies a less-than-full-rank reference cell coding.
REFERENCE: specifies a reference cell encoding. You can choose the reference value by specifying an option for a specific variable or set of variables in the CLASS statement, or you can designate the first- or last-ordered value by specifying a global-option. By default, REFERENCE=LAST.

The GLM parameterization is the default. For more information about how parameterization of classification variables affects the construction and interpretation of model effects, see the section Specification and Parameterization of Model Effects.

TRUNCATE<=n>

specifies the truncation width of formatted values of CLASS variables when the optional n is specified.

If n is not specified, the TRUNCATE option requests that classification levels be determined by using no more than the first 16 characters of the formatted values of CLASS variables.