Of course you're right Jeanette. Though running the fixed effects
won't hurt either I suppose. Whichever is easiest then.
-Tom
On Wed, May 16, 2012 at 3:42 PM, Jeanette Mumford
<[log in to unmask]> wrote:
> Hi,
>
> Using fixed effects on a zstat image isn't necessary for 2 reasons. Mostly
> because FSL only runs a fixed effects analysis if it finds copes and
> varcopes, so zstats won't have corresponding varcopes (and they don't need
> them). Secondly, if you use the first level zstat image, these are
> basically the Fisher's Z transformed correlations, which are distributed
> Normally with a sd of 1/sqrt(N-3), where N is the number of time points, so
> the variances are equal across subjects and runs. The differences in
> variances have been adjusted for. Instead, you should combine runs over
> subjects using OLS.
>
> Cheers,
> Jeanette
>
>
> On Wed, May 16, 2012 at 9:07 AM, Tom Johnstone <[log in to unmask]>
> wrote:
>>
>> Hi,
>>
>> Here would be the approach:
>>
>> 1. Run a 1st level analysis to compute connectivity maps for each
>> participant. The *ztstat* images will give a measure of connectivity
>>
>> 2. Separately for each subject, run a 2nd level fixed effects analysis
>> on the *zstat* images from the 1st level analysis. Specify a separate
>> EV for each session, and use contrasts of 1 -1 and -1 1 to compute
>> connectivity differences between sessions (and 0.5 0.5 contrast for
>> the mean connectivity). The output *copes* will represent the
>> connectivity differences
>>
>> 3. Run a 3rd level analysis (either using Flame or Randomise) to
>> perform a 1-sample t-test on the *copes* from the 2nd level analyses.
>>
>> -Tom
>>
>>
>>
>> On Wed, May 16, 2012 at 2:36 PM, Maren Strenziok
>> <[log in to unmask]> wrote:
>> > Hi Tom,
>> >
>> > what would be the input to the fixed effects 2nd level analysis? Cope,
>> > zstats images, or feat directory?
>> >
>> > Maren
>
>
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