Dear SPM experts,

Sorry for the following stupid statistics question, but it is very important to me:  I have some preliminary data (groups of 4 and 4).  Using spm8, I was able to get the contrasts of each subject, but because my groups are too small and I couldn't get any group result, how can I address the "effect size"?  After reading a bunch of statistics descriptions, I still don't have a clear understanding.  I understand in SPM8 the "plot" function can plot a voxel's effect size with an error bar, but I don't really understand what it means.  Also, if I provide the z scores on activated pixels of a representing subject,  does it address the statistical power somehow?  Could someone kindly explain or direct me in a simple way?

Thank you very much,

Wei