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Re: questions on perfroming 2 x 2 within-subjects ANOVA in SPM5

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Thu, 20 Dec 2007 21:14:45 +0100

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 ```Dear Will, Tobias, Yiquan, and Markus, Thank you for your replies. However, I am still confused about the implementation of within-subjects ANOVA in SPM5. Your design matrix seems to represent one-wayANOVA. I thought that the design matrix for two-way ANOVA should 'explicitly' model the main effects and interaction. Indeed, the one-way (your design-matrix, or Fig 5 type in 'ANOVAs and SPM') and two-way (Fig 7 type) models produced different results for the main effects and interaction. Which is more appropriate for the 2 x 2 within-subjects ANOVA? I would be very grateful for your help. Best regards, Michiru Dr. Michiru Makuuchi Max Planck Institute for Human Cognitive and Brain Sciences Stephanstrasse 1a, 04103 Leipzig, Germany Will Penny さんは書きました: > Dear Michiru, > > This is most easily done using the 'Flexible Factorial' > option. > > 1. Create two factors. > > 2. Call the the first one Subject. Independence Yes, Variance Equal. > > 3. Call the second one 'Condition'. Independence Yes, Variance Unequal. > > 4. Under, Specify Subjects or all Scans, Choose Subjects > > 5. Under Subjects, create a new 'Subject' for each subject that you have > eg. 5. > > 6. Then, for each Subject, under 'Scans'. Enter the 4 scans you have for > each subject. > > 7. Also, for each Subject, under 'Conditions' enter the vector [1:4] > > 8. Under Main effects and Interactions create 2 main effects; factor 1 > and factor 2. > > 9. Specify other covariates as necessary and your o/p directory. > > 10. Then save your design job as 'within_subject_design' and press run. > > I have attached my saved job file 'within_subject_design.mat' as a > template for you. When you run it, SPM should create the design matrix > shown in 'design-matrix.png'. > > Note the 5 subject columns on the left. Without these 5 columns > you do not have a 'within-subject' design. > > Also I have treated your 2 x 2 design as a 1 x 4. So you'll need to bear > this in mind when doing your contrasts eg. 1 1 -1 -1 and 1 -1 1 -1 to > test for main effects and 1 -1 -1 1 for the interaction (of course, > pre-pad these with 5 0's). > > Best wishes, > > Will. > Michiru Makuuchi wrote: > >> Hi, >> >> >> I have tired to perfrom 2 x 2 within-subjects ANOVA in SPM5, but I >> couldn't find >> how I could do that in 'Full factorial' dsign. Therefore I designed the >> design matrix >> via 'Multiple regression' option. The resulted design matrix was similar >> to Fig 7 of >> Henson and Penny's online document (ANOVA and SPM). The difference was >> only the position >> of constant term. In Fig 7, it was the 4th column, but it was on the >> last column in my design matirix. >> >> Here are my questions. >> Is my approach acceptible for the purpose? >> Can someone point out the exact procedure to build the model for 2 x 2 >> within-subject ANOVA? >> >> >> Best regards, >> >> Michiru >> >> Michiru Makuuchi >> Max Planck Institute >> for Human Cognitive and Brain Sciences >> Stephanstrasse 1a, 04103 Leipzig, Germany >> >> >> > > > > ------------------------------------------------------------------------ > ```