ZEROMODEL Statement :: SAS/STAT(R) 12.3 User's Guide: High-Performance Procedures

ZEROMODEL Statement

ZEROMODEL <effects> </ zeromodel-options> ;

The ZEROMODEL statement defines the statistical model for zero inflation probability in terms of model effects that are constructed from variables in the input data set. An intercept term is always included in the model.

You can specify the following zeromodel-options.

INCLUDE=n INCLUDE=single-effect INCLUDE=(effects)

forces effects to be included in all models for zero inflation for all selection methods. If you specify INCLUDE=n, then the first n effects that are listed in the ZEROMODEL statement are included in all models. If you specify INCLUDE=single-effect or if you specify a list of effects within parentheses, then the specified effects are forced into all models. The effects that you specify in the INCLUDE= option must be explanatory effects that are specified in the ZEROMODEL statement before the slash (/).

LINK=keyword

specifies the link function for the zero inflation probability. The keywords and the associated link functions are shown in Table 4.8.

Table 4.8: Built-In Link Functions for Zero Inflation Probability

	Link
LINK=	Function	$g(\mu ) =\eta =$
CLOGLOG \| CLL	Complementary log-log	$\log (-\log (1-\mu ))$
LOGIT	Logit	$\log (\mu /(1-\mu ))$
LOGLOG	Log-log	$-\log (-\log (\mu ))$
PROBIT	Probit	$\Phi ^{-1}(\mu )$

$\Phi ^{-1}(\cdot )$ denotes the quantile function of the standard normal distribution.

START=n START=single-effect START=(effects)

begins the selection process from the designated initial zero inflation model for the FORWARD and STEPWISE selection methods. If you specify START=n, then the starting model includes the first n effects that are listed in the ZEROMODEL statement. If you specify START=single-effect or if you specify a list of effects within parentheses, then the starting model includes those specified effects. The effects that you specify in the START= option must be explanatory effects that are specified in the ZEROMODEL statement before the slash (/). The START= option is not available when you specify METHOD=BACKWARD in the SELECTION statement.

The HPGENSELECT Procedure

ZEROMODEL Statement