Hello,
I would like to address the question whether or not my first level GLM fits better in certain subjects and not in others. I tested 3 different learning strategies in 3 different groups of normal subjects (each subject had 1 strategy). I have found some interesting differences between the groups/strategies, but I would like to make sure that the results that I find are based upon the differences in the experimental manipulation and not differences in the model fit. In particular, the different strategies vary slightly in their reaction times.
What I would like is something that tells me whether the fit of modelA(group1) = fit modelA(group2) = fit modelA(group3).
I have read the Rosa et al. NeuroImage 2010 paper on Bayesian model selection maps for group studies, and looked here in the Listserve both at the Bayesian model selection and at other measures of goodness of fit (e.g. Bullmore et al NeuroIamge 2000). In the Bayesian model selection an alternative model would be the null model but I am not performing a subtraction so I cannot use both regressors together as the null model. And it seems like I should be able to do something akin to a chi-squared but what data should I use? The Bullmore paper and the listserve messages regarding this method talk about SEM and not directly fMRI. I have looked at PSC in specific regions that I am interested in and at the time courses of the data, but have not done a direct comparison of the models.
If anyone has any suggestions I would greatly appreciate it.
Thanks,
Virginia
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