The COUNTREG Procedure

CLASS Statement

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

The CLASS statement names the classification variables that are used to group (classify) data in the analysis. Classification variables can be either character or numeric.

Class levels are determined from the formatted values of the CLASS variables. Thus, you can use formats to group values into levels. For more information, see the discussion of the FORMAT procedure in the SAS Language Reference: Dictionary. The CLASS statement must precede the MODEL statement.

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 that are specified in the CLASS statement. If you specify more than one CLASS statement, the global-options 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:

MISSING

treats missing values (., ._, .A, …, .Z for numeric variables and blanks for character 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. You can specify the following values:

DATA: sorts levels by the order of appearance in the input data set.
FORMATTED: sorts levels by external formatted values, except for numeric variables that have no explicit format. Those variables are sorted by their unformatted (internal) values. Ths sort order is machine-dependent.
FREQ: sorts levels by descending frequency count; levels that have more observations come earlier in the order.
INTERNAL: sorts levels by unformatted value. Ths sort order is machine-dependent.

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 Language Reference: Concepts. By default, ORDER=FORMATTED.

PARAM=EFFECT | GLM | REFERENCE

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

EFFECT: uses effect coding to create design matrix columns from the CLASS variables.
GLM: uses less-than-full-rank reference cell coding to create design matrix columns from the CLASS variables. This value can be used only as a global option.
REFERENCE: uses reference cell coding to create design matrix columns from the CLASS variables. You can abbreviate this value as REF.

All parameterizations are full rank, except for the GLM parameterization. The REF= option in the CLASS statement determines the reference level for effect and reference coding and for their orthogonal parameterizations. It also indirectly determines the reference level for a singular GLM parameterization through the order of levels. By default, PARAM=GLM.

REF=’level’ | FIRST | LAST

specifies the reference level for PARAM=EFFECT, PARAM=REFERENCE, and their orthogonalizations. When PARAM=GLM, the REF= option 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 with a singular parameterization.

For an individual variable REF= option (but not for a global 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 global or individual variable REF= 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.

Last updated: November 05, 2018