I have multiple tests done on a similar subject (brain activity in different regions of the brain) I have a treatment group and control group. When comparing the two groups, on the 12 different brain regions, the treatment group had less brain activity in every region. However, because my sample size was 8 for treatment and 14 for control only two of them was significant. Is there something I can do to say that overall although 10 of the 12 regions didnt have significant it was likely because of low sample size for those and that there is a difference between the treatment and control overall? I know I could average all of the brain regions for each participant and do a t test on that but the sample size would still be low and this wouldnt be significant.
The first thing to know is: what do you want to test ?
Is it: 1/ that the treatment has an effect on all areas of the brain ? 2/ or that the treatment has an effect on at least one area of the brain. 3/that the treatment has some kind of overall effect.
If it is 1/, it seems you cannot show it. Perhaps indeed due to sample size. Imagine the treatment has a true effect of 10 in the 2 areas where you find significant effects, but only a true effect of 3 in the other areas. With the same sample size, it is possible to find significant effects in the 2 areas, and no effect in the other 8 areas.
If it is 2/, you almost got it. You may have however to think to adjust your standard errors to "multiple hypotheses testing".
If it is 3/, why not indeed consider all observations in a same regression. In this case, I would add to the regression area-of-the-brain fixed-effects.