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I believe that if the two groups have completely separate frequencies (e.g Group 1 is all subjects w/ higher frequency), then you won't be able to adjust for the effect of frequency. Linling Li wrote: > Hi all, > It's a question I feel really confused about and hope someone could > help me with it. > I have two groups of data which all involves a same motor task. But > the two groups of subjects have different frequencies in performing > the task: one group has relatively small frequency. So if I want to > compare the functional activation of the two groups, the first thing I > need to do is to exclude the impact of different frequencies. > At first, I did one-sample t-test for each group with the subjects' > frequencies as a covariate. Then I did two-sample tests with a > frequency vector which includes the frequencies of all the subjects > (two groups) as a covariate for each group seperately. However, the > group differencies seen by comparing the one-sample t-test results of > two groups are really different from the results of two-sample t-test. > Therefore, I'm wondering if a two-sample t-test with frequency as > covariate is proper to exclude the impact of different frequencies. Or > if there is some other way to exclude different frequencies' impact? > Hope someone could help me understanding where is the problem here in > my work. > Thanks all in advance! > 2011-08-09 > ------------------------------------------------------------------------ > ÀîÁÕÁá > > Linling Li > Research Centre for Neural Engineering > -------------------------------------- > Phone: +86-755-86392232 > Email: [log in to unmask] <mailto:[log in to unmask]> > Shenzhen Institutes of Advanced Technology, > Chinese Academy of Sciences.