Dear statisticians
In classical SPM fMRI analysis beta wights are used for interpreting signal strength in the data. Regressors recieve a wigth so that the model as a whole describe the date best.
Now we are interested in the correlation between a regressor and the data. This poses the question for statistical "tightness" between regressors and the data and not the relative weigth of a regressor in a model. We further want to compare the regressor correlation between groups, asking if they differ in terms of regressor-BOLD coupling strength.
To recieve the multiple correlation from a multiple regression (GLM) is mathematically very easy. To my knowledge to automatically recieve correlation values for specific regressors is not implemented in SPM.
Why are beta wheights but not regreessor correlation of interest in general? Has someone applied fMRI analysis on correlation corefficients? Is there a reason why such an analysis would not make sense?
Thank you for any comments
Rafael
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