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The F-test tests the null hypothesis that A=B=C. It doesn't individually compare the groups. If there is an effect of group it will detect it; however, in some cases the t-test of A-C will be significant when the F-test isn't. There are two potential reasons for this: (1) The t-test is evaluated with one-tail; and (2) The F-test uses the variance based on all three groups rather than just A and C. 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 Website: http://www.martinos.org/~mclaren Office: (773) 406-2464 ===================== This e-mail contains CONFIDENTIAL INFORMATION which may contain PROTECTED HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is intended only for the use of the individual or entity named above. If the reader of the e-mail is not the intended recipient or the employee or agent responsible for delivering it to the intended recipient, you are hereby notified that you are in possession of confidential and privileged information. Any unauthorized use, disclosure, copying or the taking of any action in reliance on the contents of this information is strictly prohibited and may be unlawful. If you have received this e-mail unintentionally, please immediately notify the sender via telephone at (773) 406-2464 or email. On Tue, Jun 12, 2012 at 11:44 AM, Valentino Pironti <[log in to unmask]> wrote: > Dear Donald, > thank you. I suspected the third row was redundant. I suppose then the > comparison A vs C is done across lines. Is that correct? > Best > Valentino > >