Dear FSL experts,
I would like to ask you for help with ANOVA design based on the 1-way
between-subject ANOVA from the GLM web page:
http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/GLM#ANOVA:_1-factor_4-levels__.281-way_between-subjects_ANOVA.29
The data are connectivity distribution maps from ProbtrackX, each
tractography was started from single vertex seed with sphere sampling.
The seeds were nearby sites, so their maps have roughly similar
distribution. Prior the group stats, maps were divided by waytotal,
transformed into standard space and smoothed by Gaussian kernel with
sigma 2.5 mm.
There is one factor at three levels (with 6, 7 and 9 inputs per
factor, respectively). I used factorial design from the second example
and reduced the number of EVs and contrasts by 1. Then I was
interested in cell means, so I constructed their contrasts as
suggested in the example.
I have several questions regarding the design:
1) Is the design valid for the described data?
2) Do the cell means represent effects which are not in the two other
levels? I based this interpretation on the resulting data, which show
no overlap between any of the three cell means. This was quite
counter-intuitive to me given that the contrast includes the intercept
EV.
3) Does the global mean or intercept in the factorial design mean
anything by itself?
4) How can I construct conjunction of the three levels? (i.e. the common effect)
5) How can I test for mean effect of each level? One sample t-test
with Randomise produces very low number of permutations. Is there any
other way besides just flipping the signs? I don't think that makes
any sense in data which are by definition always zero or positive.
Thanks a lot for any comments!
Cheers
Pavel
--
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-- MUDr. Pavel Hok
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-- Laboratoř funkční magnetické rezonance
-- Neurologická klinika
-- Lékařská fakulta
-- Univerzita Palackého v Olomouci
-- Fakultní nemocnice Olomouc
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-- Laboratory of functional magnetic resonance imaging
-- Department of Neurology
-- Faculty of Medicine and Dentistry
-- Palacky University Olomouc
-- University Hospital Olomouc
-- Czech Republic
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-- I.P. Pavlova 6, 775 20 Olomouc
-- web: fmri.upol.cz
-- tel.: +420 588 443 418
-- e-mail: [log in to unmask]
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