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st: time in xtmixed


From   megan rossi <megan_rossi@msn.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: time in xtmixed
Date   Mon, 25 Mar 2013 17:06:56 +1000

Hi Stata Guru's,
Can anyone advise me on whether I need to include time variable as a categorical variable (ie. have a prefix i.) in xtmixed or can it be treated as a continous variable even though the data was collected at only three time points (evenly spaced). My research question: is depvar associated with indepvar independent of time ie. is syntax a or b most appropriate:
a) xtmixed depvar indepvar time||ptid:time,cov(uns)
or 
b) xtmixed depvar indepvar i.time||ptid:time,cov(uns)
I noticed that the stata youtube video on this doesn't include i. however it was from 9 time points, not 3.
Cheers,
Megan Rossi APD 
PhD Candidate School of Medicine, University of Queensland
Accredited Practicing Dietitian
Princess Alexandra Hospital Nutrition & Dietetic Department
m: 0402 931 441 | e: megan_rossi@msn.com 
"Let food be thy medicine and medicine be thy food." — Hippocrates (ca. 460 – 377 BC)

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