If you have a significant two-sided t-statistic, then the F-test
should will be significant for the case of 2 groups. However, most
imaging statistics are one-sided. Thus, if your statistic is
significant only for a one-sided t-test, but not the two-sided test,
then the F-test won't be significant. For three groups, a significant
two-sided t-statistic should show up as a significant F-test, but
might not if its only marginally significant at Michael pointed out.
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Office: (773) 406-2464
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