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| From | jpitblado@stata.com (Jeff Pitblado, StataCorp LP) |
| To | statalist@hsphsun2.harvard.edu |
| Subject | Re: st: mepoisson vs meqrpoisson |
| Date | Fri, 16 Aug 2013 11:52:58 -0500 |
Phil Clayton <philclayton@internode.on.net> is using both -mepoisson- and -meqrpoisson- to fit a 3-level mixed effects model and is getting inconsistent results from -mepoisson-: > I have been experimenting with the new -mepoisson- and -meqrpoisson- > commands and have found substantively different results that I can't > explain. > > ... > mepoisson inf apd, exp(duration) || hospid: || patient: > ... > meqrpoisson inf apd, exp(duration) || hospid: || patient: > ... Phil sent us a copy of the data and commands used to reproduce the problem. We have determined that -mepoisson- is suffering from a likelihood scaling problem with hospid=53, which contains 527 patients. Phil can eliminate the likelihood scaling problem by excluding this group of observations, doing so will yield consistent results between -mepoisson- and -meqrpoisson-, even between the two datasets (one being a collapsed version of the other). In diagnosing the problem, we have found a bug in the code that -mepoisson- uses to compute the mean-variance adaptive parameters. We have corrected the error and will release this fix in a future update to Stata. With this fix we have verified that -mepoisson- produces the expected results when compared to -meqrpoisson- for both datasets. --Jeff jpitblado@stata.com * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/