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Date:         Sat, 14 Aug 2010 00:24:19 -0400
Reply-To:     R B <ryan.andrew.black@gmail.com>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         R B <ryan.andrew.black@gmail.com>
Subject:      Re: MIXED interaction with contrasts
In-Reply-To:  <201008101540.o7AAktwV000446@malibu.cc.uga.edu>
Content-Type: text/plain; charset=ISO-8859-1

Charla,

I realize this response is late, but I just came across this post. If you treat "Week" as a categorical variable, then you should be able to test if there is a difference in linear trends between Group 1 and Group 3 by adding the following TEST statement:

/TEST = 'Linear Trend Contrast 1 v 3' Group*Week -3 -1 1 3

0 0 0 0

3 1 -1 -3

If you wanted to test if there is a difference in linear trends between Group 2 and Groups 1 and 3, then you would add the following TEST statement:

/TEST = 'Linear Trend Contrast 2 v 1 and 3' Group*Week 1.5 0.5 -0.5 -1.5

-3.0 -1.0 1.0 3.0

1.5 0.5 -0.5 -1.5

These recommended TEST statements are untested, so you will need to confirm that these are correct.

On another note, I suggest you consider accounting for the possible residual covariance due to repeated measures by adding a REPEATED statement (e.g., unstructured, autoregressive).

HTH,

Ryan

On Tue, Aug 10, 2010 at 11:40 AM, Charla Lopez <charla3@aol.com> wrote: > Hi there- > I would like to find out whether there is an interaction between treatment > group and time, using a special contrast of treatment group. In my example, > treatment group has 3 levels, and time has 5 levels. I am able to get the > output for the custom hypotheses, but the interaction effects seem to be > based on the default coding for treatment group. > > Here is my syntax: > > MIXED WEEKLYCIGS by GROUP > with WEEK > /FIXED = > GROUP > WEEK > GROUP*WEEK > | SSTYPE (3) > /test 'G1 v G3' group -1/2 0 1/2 > /test 'G2 v G1 and G3 ' GROUP -1/2 1 -1/2 > /PRINT SOLUTION LMATRIX/METHOD = REML > /RANDOM INTERCEPT |SUBJECT (ID). > > Any advice? > > Charla > > ===================== > To manage your subscription to SPSSX-L, send a message to > LISTSERV@LISTSERV.UGA.EDU (not to SPSSX-L), with no body text except the > command. To leave the list, send the command > SIGNOFF SPSSX-L > For a list of commands to manage subscriptions, send the command > INFO REFCARD >

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