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Re: st: Re: Interpretation of contrasts
.
I don't have the answer you asked for, but another approach. It sounds
like you have one between subject factor (3 levels) and one within
subject factor (5 levels) and you have a significant interaction to
examine further. One way to follow up an interaction is to example the
simple effects, that is, to look either within a given stress level at
each repeated measure, which reduces to a oneway repeated measures
model, or to look at a given time period between stress levels, which
reduces to a oneway anova. It sounds like you want to do the latter,
in which case just do "oneway" if time is equal to the last period.
I've read that most packages use the error term from a simple oneway
anova for testing the between subject simple effects following an
interaction in your design, although the pooled term is more often
used for testing within subject simple effects at a given between
subject level following interaction. This is due to what violations
are more often expected in behavioral research (Maxwell and Delaney,
Designing experiments and analyzing data, 2nd edition, LEA publishers).
-Dave
On Feb 13, 2008, at 7:10 AM, Janet Hill wrote:
I have a repeated measures anova with 5 repeated time periods and
the response measured at 3 stress levels and I am estimating the
model as:
wsanova resp time,id(spec) between(stress) eps
test, showorder shows there to be 54 elements in the design matrix.
My problem is that I want to look at time*stress interactions at the
last time period. I have constructed a test matrix for the
necessary constraints but I get the following error message:
. test, test(c6)
( 1) time[5]*stress[1] - time[5]*stress[2] = 0
( 2) time[5]*stress[1] - time[5]*stress[3] = 0
( 3) time[5]*stress[2] - time[5]*stress[3] = 0
Constraint 1 dropped
Constraint 2 dropped
Constraint 3 dropped
. test, test(c6) mtest(sidak)
_mtest: 0 valid tests
I can carry out this tests at other time periods.
My question is how can I carry out this particular test.
Thank you,
Janet
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David C. Airey, Ph.D.
Pharmacology Research Assistant Professor
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