ZEROMODEL
dependent variable
zero-inflated regressors / options ;
The ZEROMODEL statement is required if either ZIP or ZINB is specified in the DIST= option in the MODEL statement. If ZIP or ZINB is specified, then the ZEROMODEL statement must follow immediately after the MODEL statement. The dependent variable in the ZEROMODEL statement must be the same as the dependent variable in the MODEL statement.
The zero-inflated (ZI) regressors appear in the equation that determines the probability () of a zero count. Each of these variables has a parameter to be estimated in the regression. For example, let be the th observation’s vector of values of the ZI explanatory variables ( is set to 1 for the intercept term). Then is a function of , where is the vector of parameters to be estimated. (The ZI intercept is ; the coefficients for the ZI covariates are .) If this option is omitted, then only the intercept term is estimated. The “Parameter Estimates” table in the displayed output gives the estimates for the ZI intercept and ZI explanatory
variables; they are labeled with the prefix “Inf_”. For example, the ZI intercept is labeled “Inf_intercept”. If you specify Age
(a variable in your data set) as a ZI explanatory variable, then the “Parameter Estimates” table labels the corresponding
parameter estimate “Inf_Age”.
The following options can be specified in the ZEROMODEL statement following a slash (/):