SUPPORT / SAMPLES & SAS NOTES
Problem Note 48922: Incorrect log likelihood, type1, type3 tests for ZIP model when WEIGHT statement is specified
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When a zero-inflated Poisson (ZIP) model is requested in PROC GENMOD and the WEIGHT statement is specified, then the Log Likelihood, Full Log Likelihood, AIC, AICC, and BIC statistics in the Criteria For Assessing Goodness Of Fit table are incorrect. The parameters, standard errors and related statistics are correct. However, tests requested with the TYPE1 option and likelihood ratio tests provided by the TYPE3 option are also incorrect.
The zero-inflated negative binomial (ZINB) model is not affected.
The ZIP model can alternatively be fit using PROC COUNTREG in SAS/ETS software, or using PROC FMM or PROC NLMIXED in SAS/STAT software as illustrated in this note.
Operating System and Release Information
| Product Family | Product | System | SAS Release | |
| Reported | Fixed* | |||
| SAS System | SAS/STAT | z/OS | 9.2 TS1M0 | 9.4 TS1M0 |
| Microsoft® Windows® for 64-Bit Itanium-based Systems | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Microsoft Windows Server 2003 Datacenter 64-bit Edition | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Microsoft Windows Server 2003 Enterprise 64-bit Edition | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Microsoft Windows XP 64-bit Edition | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Microsoft® Windows® for x64 | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Microsoft Windows Server 2003 Datacenter Edition | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Microsoft Windows Server 2003 Enterprise Edition | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Microsoft Windows Server 2003 Standard Edition | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Microsoft Windows XP Professional | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Windows Vista | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Windows Vista for x64 | 9.2 TS1M0 | 9.4 TS1M0 | ||
| 64-bit Enabled AIX | 9.2 TS1M0 | 9.4 TS1M0 | ||
| 64-bit Enabled HP-UX | 9.2 TS1M0 | 9.4 TS1M0 | ||
| 64-bit Enabled Solaris | 9.2 TS1M0 | 9.4 TS1M0 | ||
| HP-UX IPF | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Linux | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Linux for x64 | 9.2 TS1M0 | 9.4 TS1M0 | ||
| OpenVMS on HP Integrity | 9.2 TS1M0 | 9.4 TS1M0 | ||
| Solaris for x64 | 9.2 TS1M0 | 9.4 TS1M0 | ||