Date: Thu, 9 Jun 2005 16:03:05 +0100
Reply-To: Jeremy Miles <email@example.com>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Jeremy Miles <firstname.lastname@example.org>
Subject: Power from MANOVA
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I am trying to use the MANOVA approach to estimate power, using SPSS 12,
which is outlied in the paper D'Amico, E. J., T. B. Neilands and R.
Zambarano (2001). Power analysis for multivariate and repeated measures
designs: a flexible approach using the SPSS MANOVA procedure. Behavior
Research, methods, instruments and computers 33(4): 479-484.
The analysis is pretty simple. Baseline and outcome measurements, two
groups, test for difference using baseline measure as covariate.
However, it ain't working. It works fine when I don't have a covariate
in, but when I put in the covariate, it all goes wrong. Specifically it
says that the effect of the group is zero (p = 1) and the power = 0.05.
Here's my code. Does anyone have any idea what's gone wrong?
MATRIX DATA variables = group rowtype_ baseline outcome
/FACTOR = group
/FORMAT = lower nodiagonal.
1 mean 0 0
1 n 400 400
2 mean 0 0.3
2 n 400 400
. sd 1 1
. corr 0.45
MANOVA outcome by group(1,2) with baseline
/MATRIX = in (*)
/POWER T (0.05) F(0.05)
/PRINT SIGNIF (MULT AVERF)
/PRINT PARAM (ESTIM) .
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