Email discussion lists for the UK Education and Research communities

## SPM@JISCMAIL.AC.UK

#### View:

 Message: [ First | Previous | Next | Last ] By Topic: [ First | Previous | Next | Last ] By Author: [ First | Previous | Next | Last ] Font: Proportional Font

#### Options

Subject:

Re: Mixed-model ANOVA

From:

Date:

Tue, 11 Sep 2007 13:42:21 -0400

Content-Type:

text/plain

Parts/Attachments:

 text/plain (74 lines)
 ```Following Fatima's lead, and at Ged's suggestion, here is a picture of my design matrix. As you can see, I've specified a main effect for subject, producing the 19, staggered, step-like columns. After these, there are four columns (the modeled interaction). The first two columns refer to the first level of the between-subjects effect. The last two columns refer to the second level of the between-subjects effect. Columns 1 and 3 refer to the first level of the within-subjects effect; Columns 2 and 4 refer to the second level of the within-subjects effect. I can test both of the within-subjects contrasts: [1 -1 1 -1] [-1 1 -1 1] I can test both of the interaction's contrasts: [1 -1 -1 1] [-1 1 1 -1] I can NOT test either of the between-subjects contratsts: [1 1 -1 -1] [-1 -1 1 1] the first 19 columns are all weighted with 0's (preceding the 4 contrast weights, above). Markus Lonsdale also posted recently with a similar problem in a PET study, I've copied his post below (sorry I couldn't figure out how to paste the URL without it going through my username): ---------------------------------------- Hi we try to analyse a PET study with 2 groups of subjects in 2 conditions. The idea is to look at group differences in each condition as well as in the response to the conditions. We have tried to model this as flexible factorial, 2 factors (subjects, conditions), 2 main effects (subjects, conditions) with an interaction between the two. (The idea is to define a contrast where we can "pick out" the subjects according to their group.) However, no contrasts are accepted by the contrast manager, not even the simple contrast "condition1 - condition2"!?! Any help is appreciated ... Markus ---------------------------------------- Thanks, Nick Quoting FATIMA HUSAIN <[log in to unmask]>: > > To second Nick Rule's post, it would be great if someone had a > solution for this problem. > I am attaching my design matrix. I can set up the following t contrast > zeros(1,24) 0 0 1 -1 (thus testing within subject factor stim1>stim2) > > but I cannot set up > > zeros(1,24) 1 -1 0 0 (between subject factor grp1>grp2) > > the answer always is "invalid contrast" > > (I am using flexible factorial, three factors, with "subject" as > first factor, group as second factor, stimulus as third factor, and > testing for main effect of the three factors). > I tried using Full factorial method but the full factorial method > does not treat subject as repeated measure. > > Fatima Husain```