|Date: ||Fri, 4 Sep 1998 10:58:55 -0500|
|Reply-To: ||"Nichols, David" <nichols@SPSS.COM>|
|Sender: ||"SPSSX(r) Discussion" <SPSSX-L@UGA.CC.UGA.EDU>|
|From: ||"Nichols, David" <nichols@SPSS.COM>|
|Subject: ||Re: one-way repeated measures|
Many of the methods available via POSTHOC in GLM are valid only for one way
independent samples designs (and some only with equal sample sizes). Thus,
the POSTHOC options are not the general way to handle multiple comparisons
in the general linear model in GLM. The place to go is to the EMMEANS
COMPARE option. This was added in Release 7.5. It allows you to obtain
omnibus tests and all pairwise comparisons among the levels of any main
effect, simple main effect, or averaged main effect in any design. In
Release 7.5, pairwise comparisons gave confidence intervals that were
Bonferroni corrected for between factors, but LSD or uncorrected for within
factors. In Release 8.0, the default for both types is LSD, but you have
Bonferroni or Sidak options for either type of factor.
In the dialog boxes, click on Options. Click on the within subjects factor
name and move it to the right side of the box. Then check the checkbox for
Compare main effects. Finally, choose your correction (Sidak's method is
more powerful than the Bonferroni and still conservative).
For those working on earlier releases of SPSS without access to EMMEANS
COMPARE, there are macros on the SPSS Web site for the one way repeated
measures case (http://www.spss.com/tech/macros/).
Principal Support Statistician and
Manager of Statistical Support
From: Jeff Mather [SMTP:Jmather@HARTHOSP.ORG]
Sent: Friday, September 04, 1998 8:38 AM
Subject: one-way repeated measures
I have a simple design with 15 subjects treated with four different
regimens. I know if I use GLM repeated measures ANOVA I can get the within
subject differences, but I can't get post-hoc comparison's (it's only set up
for between subject factors-and I have none).
To obtain multiple comparison's, I've rearranged my data so I can
run a one-way ANOVA. Here, I can get post-hoc testing, as the setup now
sees the regimen as a factor.
My question: I don't believe that any of the post-hoc tests offered
in the simple 1-way anova are designed specifically for a paired comparison.
Please let me know if I'm wrong here. What I've done is gone back to the
original data set up and performed the post-hoc tests using all the
combinations for a paired t-test, and manually adjusted the error rate by
incorporating a bonferronni correction.
this is pretty combersum. Is my line of thinking correct here, is
this the easiest way to get the post-hoc's done in a simple repeated