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re: st: Repeated measures with no between-participants vars?


From   David Airey <david.airey@Vanderbilt.Edu>
To   statalist@hsphsun2.harvard.edu
Subject   re: st: Repeated measures with no between-participants vars?
Date   Wed, 7 Jun 2006 19:49:21 -0500

I am trying to assess the way in which participants' evaluations of 3
different stimuli change over time, as indicated in a series of
measurements. I am interested in checking whether the pattern of changes
in those evaluations is different for the different stimuli.

HOW DOES THIS WORK? DOES EACH SUBJECT SEE 9 PRESENTATIONS (3 TIMES FOR EACH OF 3 STIMULI) IN RANDOMIZED ORDER? SO SUBJECT 1 MIGHT HAVE SEEN (1,1,1) (3,3,3) (2,2,2) WHEREAS SUBJECT 2 SAW A DIFFERENT ORDER. JOSEPH IS THINKING YOU WERE CAREFUL ENOUGH TO BLOCK SUBJECTS INTO ONE OF THE 6 POSSIBLE ORDERS (1,2,3; 1,3,2; 2,1,3; 2,3,1; 3,1,2; 3,2,1). SO YOU PROBABLY HAD A MUTLIPLE OF 6 SUBJECTS. BECAUSE YOU HAVE MORE THAN ONE SUBJECT PER ORDER IF THIS IS THE CASE, ORDER IS A BETWEEN SUBJECTS FACTOR. YOU CAN MODEL IT OR NOT BUT IT SHOULD HAVE BEEN PART OF THE STUDY DESIGN.


In other words, the two within-participants variables are (1) type of
stimulus, and (2) time of measurement. There are no between- participant
variables.

This seems like a simple task, but I haven't been able to get Stata to do
this for me. I tried a number of variations on the repeated ANOVA command,
but no luck. I would greatly appreciate any advice.
YOU CAN MODEL THIS WITH EITHER ANOVA, MANOVA, OR XTMIXED, IN ADDITION TO WHAT JOSEPH SAYS. FOR XTMIXED, SEE

<http://www.ats.ucla.edu/stat/Stata/faq/xtmixed.htm>

AND FOR ANOVA SEE

http://www.stata.com/support/faqs/stat/anova2.html

-DAVE
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