The ROBUSTREG Procedure

EFFECT Statement

EFFECT name=effect-type (variables </ options>);

The EFFECT statement enables you to construct special collections of columns for design matrices. These collections are referred to as constructed effects to distinguish them from the usual model effects that are formed from continuous or classification variables, as discussed in the section GLM Parameterization of Classification Variables and Effects in Chapter 19: Shared Concepts and Topics.

You can specify the following effect-types:

COLLECTION: is a collection effect that defines one or more variables as a single effect with multiple degrees of freedom. The variables in a collection are considered as a unit for estimation and inference.
LAG: is a classification effect in which the level that is used for a given period corresponds to the level in the preceding period.
MULTIMEMBER | MM: is a multimember classification effect whose levels are determined by one or more variables that appear in a CLASS statement.
POLYNOMIAL | POLY: is a multivariate polynomial effect in the specified numeric variables.
SPLINE: is a regression spline effect whose columns are univariate spline expansions of one or more variables. A spline expansion replaces the original variable with an expanded or larger set of new variables.

Table 86.8 summarizes the options available in the EFFECT statement.

Table 86.8: EFFECT Statement Options

Option	Description
Collection Effects Options
DETAILS	Displays the constituents of the collection effect
Lag Effects Options
DESIGNROLE=	Names a variable that controls to which lag design an observation is assigned
DETAILS	Displays the lag design of the lag effect
NLAG=	Specifies the number of periods in the lag
PERIOD=	Names the variable that defines the period
WITHIN=	Names the variable or variables that define the group within which each period is defined
Multimember Effects Options
NOEFFECT	Specifies that observations with all missing levels for the multimember variables should have zero values in the corresponding design matrix columns
WEIGHT=	Specifies the weight variable for the contributions of each of the classification effects
Polynomial Effects Options
DEGREE=	Specifies the degree of the polynomial
MDEGREE=	Specifies the maximum degree of any variable in a term of the polynomial
STANDARDIZE=	Specifies centering and scaling suboptions for the variables that define the polynomial
Spline Effects Options
BASIS=	Specifies the type of basis (B-spline basis or truncated power function basis) for the spline effect
DEGREE=	Specifies the degree of the spline effect
KNOTMETHOD=	Specifies how to construct the knots for the spline effect

For more information about the syntax of these effect-types and how columns of constructed effects are computed, see the section EFFECT Statement in Chapter 19: Shared Concepts and Topics.