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st: xtreg or xtmixed?


From   Johan van der Watt <jjvanderwatt@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: xtreg or xtmixed?
Date   Mon, 19 Dec 2011 11:44:06 +0200

Hi
I need to do longitudinal statistics on a panel data set of 150
individuals over 4 different time points. My dependent variable is the
development of neuropathy (everyone is neuropathy free at baseline
assessment), and a have numerous continuous independent
variables/possible risk factors for development of neuropathy, such as
CD4 count. A few of the continuous variables are not normally
distributed, and I am able to normalize most of them by either logging
or square rooting them. Further, looking at these variables over time,
some of them also do not follow a linear pattern, i.e they peak at
visit 2 or 3 then go down at visit 4.
I have used the -xtreg- command with -mle-, using a continuous
variable, such as CD4 count, Neuropathy, and Visit:

xtreg cd4_  neuropathy visit, i(patientno2) mle

but after reading online articles and bulletin boards,  I have also
tried the mixed effects model:

xtmixed cd4_  neuropathy visit ||  patientno2:,mle

As I am a stats amateur, is this what I am doing correct? Any other options?

Thanks

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