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Hi Mayuresh,

just edit the cg_vbm8_spmT2x.mat or cg_vbm8_spmF2x.mat and you will find the respective formula for calculating effect size within the first few lines of the files.

Good luck!
Raphael

Am 30.05.2011 07:25, schrieb Mayuresh K:
[log in to unmask]" type="cite">Thanks Raphael and Alexa for your inputs!

Raphael - Do you know of any documentation how the effect size is calculated using the "threshold and transform" option?
I would imagine it is valid to use this option for fMRI T maps as well?

Thanks,
Mayuresh



On Fri, May 27, 2011 at 9:05 PM, Raphael Hilgenstock <[log in to unmask]> wrote:
Hi Mayuresh,

you might want to use the "threshold and transform spm-t/F-maps" option as implemented in the VBM8 toolbox (http://dbm.neuro.uni-jena.de/software/) which allows you to calculate effect size measure 'd' for the respective spm-volume. I hope this helps.

Best regards
Raphael

Am 27.05.2011 08:21, schrieb Mayuresh K:

Hello spm experts,

Could anyone guide me how to do a power analysis using fMRI or VBM data? I have performed a random effects analysis comparing two groups of subjects using their fMRI and VBM data. I have found a number of regions with significant differences for both data sets.
I can probably calculate the mean and standard deviation of the %signal change (or volume) for each group for the peak voxels say in a particular anatomical region. Then use these to calculate effect sizes and power - Is this a valid approach?
Any other suggestions welcome.

Thanks,
Mayuresh