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>
Subject: Re: model comparison
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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.
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.