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Mike - If you do a one-way ANOVA with 4 conditions then strictly speaking you won't be able to specify the right variance components for the nonsphericity 'correction' in SPM2 (this may not be true of SPM5 but I'm not sure if it's 'in' yet-?) - however you could do it by hand and adjust SPM.xVi.Vi, or you could simply select the full nonsphericity options as if both factors were within subjects, and hope that the estimated covariances between the conditions that are from different subjects is near zero (as they should be zero!). Here and in the regression model (in which I don't think there's a nonsphericity option) your T-contrast of [-1 1 1 -1] would give you the interaction where drug - placebo effects are bigger in the controls than in the patients. You'd need to do [1 -1 -1 1] for the other direction. (I'm not sure what you mean by 'AND' here) The other way to do it with no compromise or hacking is simply to do the drug-placebo contrasts at the first level as you originally suggested (if you have put them into a single design matrix for each subject as 2 sessions) and take this up to the 2nd level for 1- (for effects within group or overall) and 2- (for group differences) sample t-tests . This is slightly different from putting everything in a 2nd level mixed ANOVA because it effectively tests each effect against its own error term - see various postings by Rik Henson, e.g. http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0507&L=SPM&P=R11001&I=-3&X=29 B1D5211551440611&Y=amm96%40cam.ac.uk for more detail - but either is correct, that's just a matter of preference. Hope this helps Alexa | -----Original Message----- | From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]On | Behalf Of Mike Angstadt | Sent: 28 July 2005 15:28 | To: [log in to unmask] | Subject: Re: [SPM] mixed between/within subject RFX | | | Okay, so the suggestions made to me included either performing a multiple | regression with columns for diagnosis, treatment, and the interaction, or | performing a one-way ANOVA with 4 conditions. | | What do SPMers think is the more appropriate way to get close to a 2-way | ANOVA result? | | In the regression case with 3 columns: | first: 1's for Drug, -1's for Placebo | second: 1's for Patients, -1's for Controls | third: first*second interaction | If I do a T-contrast of [1 0 0] that should show activations | where Drug was | greater than Placebo correct? | what about a T-contrast of [0 0 1]? Is that (Drug > Placebo) AND | (Patient > Control), or does it just show areas where there was a | differential effect of treatment based on diagnosis (without letting me | know the direction)? | | For the One Way ANOVA with 4 conditions: | Condition 1: Patients_Drug | Condition 2: Patients_Placebo | Condition 3: Controls_Drug | Condition 4: Controls_Placebo | In order to get for example (Patients > Controls) AND (Placebo > Drug) | would I use a T-contrast of [-1 1 1 -1]? (basically doing a double | subtraction, (-1 +1) - (-1 +1)) | | Thanks | -Mike | | At 10:55 AM 7/27/2005 -0400, Andrew J. Saykin wrote: | >Mike, | > | >You could also use a regression model with main effects for | diagnosis and | >treatment and include an interaction term for diagnosis X treatment | >effects since these are likely of particular interest in your study. As | >an example, we used this approach in our donepezil study (Brain 2004; | >127:1574-83). | > | >Andy Saykin | > | > | > | >At 10:23 AM 7/27/2005, Mike Angstadt wrote: | >>Hi, | >> We're looking for the best way to analyze a design like the | >> following: | >> - Two groups of subjects (ex: patients and controls) | >> - two levels of treatment (ex: drug and placebo) | >> Each subject has 2 scans from separate days. One for the drug | >> condition and one for placebo. What's the easiest and/or best way to | >> look at the group RFX? | >> One idea we had was to just model both scans in one | large design | >> matrix (as in this post | >> | http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0502&L=SPM&D=0&I=-3 | &X=334B9904DDB400BF3B&Y=&P=15311) | >> But we weren't sure if that was the best way. | >> Since SPM2 doesn't offer a 2-way ANOVA, what's the best option | >> to run something like that? Is there a script someone has to | make SPM2 | >> do a 2-way? Or could I fake it with a one-way ANOVA with 4 conditions | >> (ex: patient_drug, patient_placebo, control_drug, control_placebo)? | >> | >> Thanks | >> | >>-Mike | > | > | > | >======================================================== | >Andrew J. Saykin, PsyD, ABPP | >Professor of Psychiatry and Radiology | >Director, Neuropsychology Program and Brain Imaging Laboratory | >Department of Psychiatry - DHMC | >Dartmouth Medical School | >Lebanon, NH 03756 | > | >Tel. (603) 650-5824 | >Fax (603) 650-5842 | > | >email:[log in to unmask] | > | >http://synapse.hitchcock.org | > | >======================================================== | > | >IMPORTANT NOTICE REGARDING THIS ELECTRONIC MESSAGE | >This message is intended for the use of the person to whom it is | addressed | >and may contain information that is privileged, confidential, and | >protected from disclosure under applicable law. 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