Date:         Wed, 11 Nov 2009 10:13:20 -0500
Reply-To:     Amanda Bertram <abertra3@JHMI.EDU>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Amanda Bertram <abertra3@JHMI.EDU>
Content-Type: multipart/alternative;

I am trying to run a logistic regression and when I do I get the following errors...



For split file Unit = Hal 5 and Hal 6, there are 419 (39.1%) cells (i.e., dependent variable levels by subpopulations) with zero frequencies.

For split file Unit = Hal 5 and Hal 6, unexpected singularities in the Hessian matrix are encountered. This indicates that either some predictor variables should be excluded or some categories should be merged.

The NOMREG procedure continues despite the above warning(s). Subsequent results shown are based on the last iteration. Validity of the model fit is uncertain.



Now, the "zero frequency" warning I have been ignoring because I needed to use the zeros to calculate mean, so I am assuming they would be included in this type of regression.

Where I am really unclear is the "unexpected singularities in the Hessian matrix are encountered. This indicates that either some predictor variables should be excluded or some categories should be merged" warning. I am not sure what it means or what I do to go about fixing it.

I would appreciate any help anybody can give me.

Thanks,




Amanda Bertram, MS
Sr. Research Program Coordinator
Department of Medicine
Division of General Internal Medicine
Johns Hopkins Outpatient Center, Room 7164
601 North Caroline Street
Baltimore, MD 21287
410.955.1120    fax: 410.614.1195
abertra3@jhmi.edu<mailto:abertra3@jhmi.edu>




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