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 zeromodeloptions.

INCLUDE=n
INCLUDE=singleeffect
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=singleeffect 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 8.9.
Table 8.9: BuiltIn Link Functions for Zero Inflation Probability

Link


LINK=

Function


CLOGLOG  CLL

Complementary loglog


LOGIT

Logit


LOGLOG

Loglog


PROBIT

Probit


denotes the quantile function of the standard normal distribution.

START=n
START=singleeffect
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=singleeffect 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.