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Date:         Sun, 17 Jan 2010 19:12:28 -0800
Reply-To:     Ryan <ryan.andrew.black@GMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Ryan <ryan.andrew.black@GMAIL.COM>
Organization: http://groups.google.com
Subject:      Re: model comparison
Comments: To: sas-l@uga.edu
Content-Type: text/plain; charset=ISO-8859-1

On Jan 17, 2:29 am, Ching <kcwo...@gmail.com> wrote: > Hi everyone. > > I've done some reading about halving the p-value (difference in -2LL) > when comparing 2 different models produced by proc mixed. Is it more > appropriate this way? but why? > > Your advice is greatly appreciated. Have a great day.

Ching,

To be clear, the difference in -2 log likelihoods approximates a Chi- Square distribution with degrees of freedom equal to the difference in the # of estimated parameters for each model. The assumption of this test is that one model is nested within the other model. In response to your question, I have never heard of halving the p-value associated with this Chi-Square test.

Ryan


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