Dear Michiru,
Michiru Makuuchi wrote:
> 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.
>
They should'nt produce different results.
The main concept here is that you can either
1) Specify a design matrix with 'condition' variables (fig 5) and then
use contrasts [1 1 -1 -1], [1 -1 1 -1] to test for main effects and
[1 -1 -1 1] for the interaction
OR
2) Specify a design matrix with 'main effects and interactions' as
variables (fig 7) and then use contrasts [1 0 0 0], [0 1 0 0] for the
main effects and [0 0 1 0] for the interaction.
The should both give you the same results (notice how application of the
contrast vectors in (1) to the columns of the design matrix in fig 5
give you the same vectors as application of the contrasts in (2) to the
columns in fig 7).
Best wishes,
Will.
> 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
>>>
>>>
>>>
>>
>>
>> ------------------------------------------------------------------------
>>
>
>
--
William D. Penny
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7475
FAX: 020 7813 1420
Email: [log in to unmask]
URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
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