Hi,
We're trying to understand Randomise in some detail, both using TBSS and
applying it to some perfusion images, and for SIENA. Impressive program. But
we have several questions:
1. Matrix design. The GLM procedure for matrix creation outputs the design
and contract matrices, but not the headers for those files. We're not clear
about:
/NumWaves 2--What does this mean?This is from an unpaired two-sample t-test.
/NumPoints 24--OK
/PPheights 1 1--peak to peak heights? What does this mean? This is from an
unpaired two-sample t-test.
And are these /comments input into the program, or are they strictly
informational comments?
2. There are several types of output images.
<output>_vox_tstat
--when would you accept these results as valid, i.e. is there ever a case
when the lack of multiple comparisons corrections is acceptable?--see next
question for related part of this.
<output>_max_tstat
--what is the extent of the multiple comparisons? is there a way to find out
the number of comparisons being run and corrected for? our statistician
suggested that it may be useful to know, even an approximate value, to
inform thinking about the number of permutations entered into Randomise in
the first place.
<output>_maxc_tstat
--we don't get the cluster approach. is this also a way to increase power by
decreasing sample size? what is empirical experience on FA image analysis of
useful cluster size?
Thank you in advance for all your work on FSL, it is a tremendous program.
Rob
|