PROC COUNTREG: MODEL Statement :: SAS/ETS(R) 9.22 User's Guide

The COUNTREG Procedure

MODEL Statement

MODEL dependent = <regressors> </ options> ;

The MODEL statement specifies the dependent variable and independent covariates (regressors) for the regression model. If you specify no regressors, PROC COUNTREG fits a model that contains only an intercept. The dependent count variable should take on only nonnegative integer values in the input data set. PROC COUNTREG rounds any positive noninteger count values to the nearest integer. PROC COUNTREG ignores any observations with a negative count.

Only one MODEL statement can be specified. The following options can be used in the MODEL statement after a slash (/).

DIST=value

specifies a type of model to be analyzed. If you specify this option in both the MODEL statement and the PROC COUNTREG statement, then only the value in the MODEL statement is used. The following model types are supported:

POISSON | P: Poisson regression model
NEGBIN(P=1): negative binomial regression model with a linear variance function
NEGBIN(P=2) | NEGBIN: negative binomial regression model with a quadratic variance function
ZIPOISSON | ZIP: zero-inflated Poisson regression. The ZEROMODEL statement must be specified when this model type is specified.
ZINEGBIN | ZINB: zero-inflated negative binomial regression. The ZEROMODEL statement must be specified when this model type is specified.

NOINT

suppresses the intercept parameter.

OFFSET=variable

specifies a variable in the input data set to be used as an offset variable. The offset variable appears as a covariate in the model with its parameter restricted to 1. The offset variable cannot be the response variable, the zero-inflation offset variable (if any), or one of the explanatory variables. The Model Fit Summary gives the name of the data set variable used as the offset variable; it is labeled as "Offset."

Printing Options

CORRB: prints the correlation matrix of the parameter estimates. The CORRB option can also be specified in the PROC COUNTREG statement.
COVB: prints the covariance matrix of the parameter estimates. The COVB can also be specified in the PROC COUNTREG statement.
ITPRINT: prints the objective function and parameter estimates at each iteration. The objective function is the negative log-likelihood function. The ITPRINT option can also be specified in the PROC COUNTREG statement.
PRINTALL: requests all printing options. The PRINTALL option can also be specified in the PROC COUNTREG statement.

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