Stata The Stata listserver
[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

Re: st: repeated measures design


From   Joseph Coveney <jcoveney@bigplanet.com>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   Re: st: repeated measures design
Date   Thu, 20 Nov 2003 23:30:55 +0900

Jim Seward wrote:

----------------------------------------------------------------------------

I have some data for for subjects which includes repeated administrations
of the MMSE (a test of mental status that is usually considered a
continuous variable) and repeated lab values (see below);


ID   Lab value a    Lab value b    MMSE
1         #         #      #
1         #         #    #
1
1         and so on...

2
2
2

3
3
3
3

4
4

I want to see if the MMSE scores vary in any systematic way with the lab
values.  Note that there are some subjects with 4 observations, some with
3, and some with 2.

I essentially want to do a repeated measures multiple regression, with MMSE
as the outcome variable.

Is there such a thing?

----------------------------------------------------------------------------

Assuming that the two types of laboratory test results are not intolerably
correlated, how about -xtreg MMSE lab_value_a lab_value_b, i(ID) fe-?  Based
on my understanding of the pitfalls of using random-effects (mixed-effects)
regression, I do not recommend -xt , re- for this, since I expect that the
laboratory test results will correlate with the random effect.

Graphical examination of the data is often helpful, and would seem
especially so here.  Perhaps with a scatterplot matrix (-graph matrix MMSE
lab_value_a lab_value_b-), it will become evident if the MMSE scores
systematically vary with laboratory test results, and with time or sequence.

Joseph Coveney





*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index