The CAUSALTRT Procedure

CLASS Statement

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

The CLASS statement names the classification variables to be used as explanatory variables in the analysis.

The CLASS statement must precede the MODEL and PSMODEL statements. Most options can be specified 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 specified in the CLASS statement. However, individual CLASS variable options override the global-options. Unless otherwise indicated, you can specify the following values for either an option or a global-option:

CPREFIX=n

uses at most the first n characters of a CLASS variable name in creating names for the corresponding design variables. The default is 32 minus min left-parenthesis 32 comma max left-parenthesis 2 comma f right-parenthesis right-parenthesis, where f is the formatted length of the CLASS variable.

DESCENDING
DESC

reverses the sort order of the classification variable. If both the DESCENDING and ORDER= options are specified, PROC CAUSALTRT orders the categories according to the ORDER= option and then reverses that order.

LPREFIX=n

uses at most the first n characters of a CLASS variable label in creating labels for the corresponding design variables. The default is 256 minus min left-parenthesis 256 comma max left-parenthesis 2 comma f right-parenthesis right-parenthesis, where f is the formatted length of the CLASS variable.

MISSING

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

ORDER=DATA | FORMATTED | FREQ | INTERNAL

specifies the sort order for the levels of classification variables. This ordering determines which parameters in the model correspond to each level in the data.

The following table shows how PROC CAUSALTRT 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. The sort order is machine-dependent.
FREQ Descending frequency count. Levels that have more observations come earlier in the order.
INTERNAL Unformatted value. The sort order is machine-dependent.

By default, ORDER=FORMATTED. For more information about sort order, see the chapter on the SORT procedure in the Base SAS Procedures Guide and the discussion of BY-group processing in SAS Programmers Guide: Essentials.

REF='level' | FIRST | LAST

specifies a level of the classification variable to be put at the end of the list of levels. This level thus corresponds to the reference level in the usual interpretation of the linear estimates that have a singular parameterization.

You can specify the following values:

'level'

specifies the level of the variable to use as the reference level. Specify the formatted value of the variable if a format is assigned. You cannot specify 'level' as a global-option.

FIRST

designates the first ordered level as reference.

LAST

designates the last ordered level as reference.

By default, REF=LAST.

TRUNCATE<=n>

specifies the length (n) of variable values to use in determining the CLASS variable levels. The default is to use the full formatted length of the CLASS variable. If you specify this option without the length n, the first 16 characters of the formatted values are used. When formatted values are longer than 16 characters, you can use this option to revert to the levels as determined in releases before SAS 9. The TRUNCATE option is available only as a global-option.

Last updated: December 09, 2022