Type of Tool  SAS Macro 
Title  ZIP Check Fit 
Programmer/Email  YinglinXia 
Contributing Site  Rochester 
Description 
ZIP Check Fit is a macro that tests for goodness of fit when modeling count data in the presence of a preponderance of zeros. It first checks the distribution for all variables (response and covariates) of interest and plots the distribution of response variable, and then compares the ZeroInflated Poisson (ZIP) Model with the Poisson Model using the Vnong test. Finally, the final ZIP full and null models are fitted and tested using ChiSquared test. The SAS PROC GENMOD is used to carry out the test and modeling. Vuong (1989) developed a statistic test for comparing two statistical models. This test is widely used for comparing two competing models for better fit for count data. As described in Long (1997), this statistic has a standard normal distribution, with a large positive (negative) value favoring one (the other) distribution, and a value close to zero indicating that neither model fits the data well. In this Macro, the test is implemented in such a way that a large positive (negative) value favors the ZIP (Poisson); if the Vuong statistic V is greater (less) than 1.96 (1.96), the ZIP (Poisson) is preferred. 
Example  Example code 
Classification Graph Type 

References 
Long, J. S. (1997). Regression Models for Categorical and Limited Dependent Variables. Thousand Oaks, CA: Sage Publications. Vuong, Q. H. (1989). Likelihood ratio tests for model selection and nonnested hypotheses. Econometrica 57: 307–333. 
Datasets 

Data 

Software Program  SAS 
Software  SAS 
Macro Parameters 
The macro parameters are as follows: DSname =name of SAS data set DepVar =name of outcome variable ClassVar =name of categorical variable(s) IndepVar =name of predictor variable(s) ZeroInflatVar =name of zero inflated variable format =output format 
RCode  Attachment 

RCode 

SASCode  Attachment  Rochester_Zip Check Fit_Main Macro 
SASCode 

StataCode  Attachment 

StataCode 

Other Code  Attachment 

Other Code 

Called Data Manipulation 

Called Tool/Utility 

Called Checking Macro 

Called Other 

CreationDate 

RevisionDate  September 09, 2010 
Example Code  SAS Example Code 
Example Output  SAS Example Output 
SAS Examples 

SAS_Example_Code  Rochester_ZIP Check Fit_SAS Example Code 
SAS_Example_Output 
Rochester_ZIP Check Fit_SAS Example Output RTF Rochester_ZIP Check Fit _SAS Example Output html Rochester_ZIP Check Fit_SAS Example Output mht 
R Examples 

R_Example_Code 

R_Example_Output 

Stats Examples 

Special Features 

Special Features Attached 

Special Features Text 

Notes1Legend  Section with calls to needed macros 
Notes1 

Notes2Legend  Macro call with fully specified parameters 
Notes2 

Notes3Legend  Section with definitions of global macro parameters 
Notes3 

Notes4Legend  Section with definitions of local macro variables 
Notes4 

See Also 

Checklists 

Stat Tools Disclaimer  This SAS macro is developed by Dr. Yinglin Xia in consultation with Dr. Xin Tu and other members in the Department of Biostatistics and Computational Biology at the University of Rochester under the auspice of the CTSI BERD with the intent to facilitate data analyses and reporting in clinical and related research. It is copyrighted by Dr. Yinglin Xia, September, 2010 and distributed for free public access. The development of this macro was supported in part by an NIH grant R21/R33 DA027521. 
Discliamer 
The views expressed within CTSpedia are those of the author and must not be taken to represent policy or guidance on the behalf of any organization or institution with which the author is affiliated. 
Permission 
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF ERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT OLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. 
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