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Nicole,

Please see responses below.

On Tue, Jun 11, 2013 at 7:48 AM, Nicole Van Hoeck <[log in to unmask]>wrote:

> Dear SPM-users,
>
> My design looks like this:
> within subject design
> 1 group
> 1 factor with 3 levels (1A, 1B, 1C)
> 3 covariates: for each covariate I have one score per subject (testscores
> on executive funtion assessments)
>
> 3 questions:
>
> 1) When you use a one way within subject Anova in SPM is the spericity
> assumption always violated? (the bar underneath the design matrix is grey)
>

>>> The gray matrix below the design matrix represents the dependency of
the data. If a box is grey, then the estimated beta for this column is
dependent on the other betas with grey boxes. Sphericity is a difference
issue that may or may not be violated in your case. Sphericity means that
the covariances between different levels are all equal.


>
> 2) How do I create on 1st level a conjunction image of 1A&1B? (related to
> questions 3)
>

>>> You need to enter con_ images in the group map, so a conjunction is not
possible. You could try to combine the betas by addition though.

>
> 3) I'm not sure how to incorporate the covariates.
> - I would like to know how the score on the executive functions assessment
> correlate with the activation patters of the following contrasts: 1A-1C,
> 1B-1C, and the conjunction of 1A&1B
> - for example: one sample t-test (one covariate) with contrast "0 1" gives
> different results than multiple regression (3 covariates) with contrast "0
> 1 0 0"
>

>>> Covariates will not change the relationship between the 3 levels; as
such, I would recommend not including any covariates. Given your specific
questions. I would form the contrasts of of your comparisons at the
first-level, then use a one-sample t-test with a single covariate. Then
assess with the covariate is significant.

>
> Thank you so much for your help,
>
>
> Nicole
>