 |
 |
Dear colleagues, unfortunately, I am sort of naive, from a statistical point of view. Some simple questions: The experiment is the following: three different groups performed a standard encoding task. I am interested in activation differences between these groups. For that, I used a ANOVA design, 1 factor with 3 levels (group 1, group 2, group 3). QUESTION 1: Is that appropriate? To look at general group differences, I used the following F-contrast 1 -1 0 1 0 -1 0 1 -1 This gave one nice cluster. In my opinion, this means that at least two groups have activation differences in this cluster. QUESTION 2: Is that the correct interpretation? Now I wanted to find out which groups differ. I used, as post-hoc t-tests, simple t-contrasts and found out that group 1 has more activity than group 3 in the nice cluster from above. However, these t-contrasts showed also other activation differences between the groups. I assume however that I am not allowed to take these differences as "statistical real" since they did not appear in the ANOVA F-contrast. QUESTION 3: Is that correct? At last, I still did not know how to interpret these group differences. It might be that - both groups have activation, one more than the other. - both groups have deactivation, one more than the other. - one group has activation, the other deactivation. This is probably not unimportant to know. I tried several options: 1.) I used the "plot button", fitted response, against scan/time. This showed me nicely that group 1 differs from group 3, but I had a bad feeling: I did not know whether to use the "adjusted" or "fitted" response, I did not know how to extract the data from the graph, I did not know what SPN does to the data, etc. 2.) I used the "eigenvariate button" to extract the first eigenvariate from all voxels within my cluster. This gave totally different results. Does it only work when I want to look at a real time series? 3.) I decided to go back to the raw data, extracted the mean intensity value in the cluster from the con-images of all subjects. Again, I got different results QUESTION 4: what is the right way to proceed? Best wishes, Henrike -- GMX startet ShortView.de. Hier findest Du Leute mit Deinen Interessen! Jetzt dabei sein: http://www.shortview.de/?mc=sv_ext_mf@gmx