 |
 |
LLN, le 24/01/07 Dear Lena, Here is what I suggest: (1) compute all your 1-level contrasts (e.g., [activation-baseline]) for each subject individually, (2) port the corresponding con_* files to 2-level analyses using: - 1-sample t-tests with a contrast set at [1] for each group separately; - 2-sample t-tests with your two groups and a contrast set at [1 -1] (or [-1 1] depending on what you're looking at). May I also suggest to be careful with the "direction" of your subtractions, both for the group effect ([patients-controls] or [controls-patients]) and the task effect ([activation-baseline] or [baseline-activation]). Especially for the latter, be sure that you really do expect some areas to be more activated in the baseline than in the "activation" task... Hope this helps, Mauro. >Dear SPM:ers, > >I have a dataset with two groups, patients and controls. These have two >conditions, baseline and activation. It's probably simple, but I seem to >have a problem choosing the correct SPM design type for this study. I >want to look at several things: > >* Compare controls, baseline vs. activation >* Compare patients, baseline vs. activation >* Compare baseline, controls vs. patients >* Compare activation, controls vs. patients > >I thought "multi-group: conditions & covariates" would be the correct >one for all of these, but SPM won't let me put "0" to exclude columns >when I specify the contrast. Do I have to choose a separate design for >all four of these analyses? Please help. > >Thank you! > >Best regards, >Lena Edström -- _____________________________________ Help fighting hunger: http://www.hungersite.com Just click your mouse and sponsors of The Hunger Site donate a serving of food to a person in need - at no cost to you. ______________________________________ Mauro PESENTI Research Associate, National Fund for Scientific Research (Belgium) Unite de Neurosciences Cognitives Departement de Psychologie Universite Catholique de Louvain Place Cardinal Mercier, 10 B-1348 Louvain-la-Neuve tel.: +32 (0)10 47 88 22 fax: +32 (0)10 47 37 74 E-mail: [log in to unmask] http://www.nesc.ucl.ac.be http://www.nesc.ucl.ac.be/mp/pesentiHomepage.htm