Dear Freesurfers,
Sorry if the question sounds too basic.
1. I am running an analysis on qdec with paired groups - normal and patients, To control for IntraCranialVolume(ICV),I am adding it as an 'nuisance factor',Is it correct? The suggested mode to add ICV to the tabled was to *demean* the ICV. But when I subtract the mean values from individual subject ICV values,I noticed that some of the subjects have a negative demeaned ICV value. My question is - How should I proceed to include the data,ignore the negative sign(because I thought a negative ICV makes no sense) and just keep the values or retain the numbers with the sign. Please correct me if I am going wrong in any of the steps. However,I ran two analysis - one with the sign retained and other with sign removed ,I noticed that both have very different results.
2. If I want to see the effect due to lithium within the patient group (Between patients with and without psychosis) how should I design the matrix in GUI. I designed the following format Fixed factor :- Diagnosis - Psychotic-pt Non-Psychotic-pt Co-variate :- Lithium use :- 1 - lithium user 0 - non user Nuisance factor :- ICV Is this design correct? If not how should I construct it ? Also what query would contain the result for anticipated question My intention is to control for Diagnosis and then see effect/change due to lithium use.
Thank you very much
1. It is not a problem that some of the demeaned ICV values are negative; this is what happens when you demean a set of numbers; you must leave the negative numbers there. Are you doing a paired analysis or do you just have two groups? I don't think you can do a paired analysis in QDEC.
2. would this give you 3 groups (controls, patients with lithium, patients without)? If so, you cannot use QDEC for this.
If you can't use QDEC, you'll have to use the command line stream and either set up your own FSGD file or your own design matrix
On 08/04/2016 01:36 PM, Vikas Bandalli wrote:
Dear Freesurfers,
Sorry if the question sounds too basic.
- I am running an analysis on qdec with paired groups - normal and
patients, To control for IntraCranialVolume(ICV),I am adding it as an 'nuisance factor',Is it correct? The suggested mode to add ICV to the tabled was to _demean_ the ICV. But when I subtract the mean values from individual subject ICV values,I noticed that some of the subjects have a negative demeaned ICV value. My question is - How should I proceed to include the data,ignore the negative sign(because I thought a negative ICV makes no sense) and just keep the values or retain the numbers with the sign. Please correct me if I am going wrong in any of the steps. However,I ran two analysis - one with the sign retained and other with sign removed ,I noticed that both have very different results.
- If I want to see the effect due to lithium within the patient group
(Between patients with and without psychosis) how should I design the matrix in GUI. I designed the following format Fixed factor :- Diagnosis - Psychotic-pt Non-Psychotic-pt Co-variate :- Lithium use :- 1 - lithium user 0 - non user Nuisance factor :- ICV Is this design correct? If not how should I construct it ? Also what query would contain the result for anticipated question My intention is to control for Diagnosis and then see effect/change due to lithium use.
Thank you very much
-- Vikas B. R. Medical student Bangalore Medical College and Research Institute (BMCRI), Bangalore,India, Ph : +918904286825
freesurfer@nmr.mgh.harvard.edu
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Douglas N Greve -
Vikas Bandalli