Dear all,
I am trying to understand the conjunction analysis in SPM and whether it is an appropriate method for my research question.
In SPM, there is the conjunction null and the global null. I am wondering what each is doing and what interpretation can be drawn from the global null vs. the conjunction null. I couldn't find a clear answer to my question in the mailing list.
From my very simple understanding of Friston et al., 2005 (Neuroimage) (https://doi.org/10.1016/j.neuroimage.2005.01.013), the conjunction analysis shows the overlapping area where BOTH contrasts separately are significant (i.e. each contrast is significant on its own, and this is the area of overlap, like a logical AND between maps).
Does the global null hypothesis show clusters where the COMBINED effect of the two conditions become significant (separately, the two conditions may not reach significance, and only when adding their effects together do they become significant).
Ultimately, I would like to show where two contrasts both have an effect on brain change, where they have separate effects, as well as where they only have an effect when combined together (the whole is greater than the sum of their parts). If you have a suggestion for a better way of analysing the data to answer this question, we would be very grateful!
Best,
Helyne
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