Dear All,
I am using the 3dttest++ for comparing two different groups of subjects and would like to control for the effect of gender as a covariate. I referred to the help file of the 3dttest and found the following illustration on the structure of the output:
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STRUCTURE OF THE OUTPUT DATASET ~1~
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* The output dataset is stored in float format; there is no option
to store it in scaled short format :)
* For each covariate, 2 sub-bricks are produced:
++ The estimated slope of the beta values vs covariate
++ The t-statistic of this slope
++ If there are 2 sets of subjects, then each pair of sub-bricks is
produced for the setA-setB, setA, and setB cases, so that you'll
get 6 sub-bricks per covariate (plus 6 more for the mean, which
is treated as a special covariate whose values are all 1).
++ Thus the number of sub-bricks produced is 6*(m+1) for the two-sample
case and 2*(m+1) for the one-sample case, where m=number of covariates.
* For example, if there is one covariate 'IQ', and a two sample analysis
is carried out ('-setA' and '-setB' both used), then the output
dataset will contain the following 12 (6*2) sub-bricks:
#0 SetA-SetB_mean = difference of means [covariates removed]
#1 SetA-SetB_Tstat
#2 SetA-SetB_IQ = difference of slopes wrt covariate IQ
#3 SetA-SetB_IQ_Tstat
#4 SetA_mean = mean of SetA [covariates removed]
#5 SetA_Tstat
#6 SetA_IQ = slope of SetA wrt covariate IQ
#7 SetA_IQ_Tstat
#8 SetB_mean = mean of SetB [covariates removed]
#9 SetB_Tstat
#10 SetB_IQ = slope of SetB wrt covariate IQ
#11 SetB_IQ_Tstat
I believe the output I would need to explore is sub brick #1, which states SetA-SetB_Tstat and demonstrates group mean differences. My understanding was that the term 'removed' in [covariates removed] means that the covariate is controlled for in this comparison. I would be thankful if you could please confirm.
Thank you so much.
Sanaz
