Hello,
I would like to run a simple 2 sample t-test with a nuisance variable, and
also run a linear regression on TBSS data.
From what I've read in the manuals and the mail list, I think I have
formulated the correct steps, but I would like to double check in particular
the steps to create the design matrix and contrast files. Hopefully others
can also benefit from having this info all together in one message! (I
apologize beforehand for the long message! and any lack of clarity!)
After running all the tbss scripts,
For Simple 2 sample t-test:
- create design matrix and contrast files using the design_ttest2 command
For Simple 2 sample t-test w/ 1 nuisance variable:
- take the files from above and open them with a text editor
- for the .mat file, add a new column of values under Matrix for your
nuisance variable (mean-centred)
- also change NumWaves to 3, and add a value to PPheights for the difference
between the highest and lowest values of your nuisance variable
- for the .con file, add a 0 to the end of each contrast
- resulting tstat1 will show areas with higher FA in group 1, tstat2 shows
areas higher in group 2
For regression
- use the same method as above for creating the nuisance variable
- if you are interested in interactions between group and a variable, split
it to two regressors each containing variable values for one group and zeros
for the other group
- for the .con file, use a 1 to test for positive slopes, -1 to test for
negative slopes, and for interactions use a 1 and -1 for the two interaction
regressors
- resulting tstats will show areas with FA positively or negatively related
to your regressor (for contrasts simply consisting of 1 or -1) or areas
where one group's FA is related differently to your regressor (for contrasts
with 1 and -1 for interaction regressors)
Please let me know if there are any mistakes with this procedure!
Thanks,
- Jerry
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