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Thank you both so much! On 4 December 2016 at 12:12, Anderson M. Winkler <[log in to unmask]> wrote: > Thanks Andreas, I was trying to find this link with no success! > > On 3 December 2016 at 10:27, Andreas Bartsch <[log in to unmask]> > wrote: > >> Hi, >> >> also note that F-tests have a spherical or elliptical rejection region >> while individual t-tests evaluate rectangular rejection regions. This leads >> to differences in the rejection regions: points outside an ellipse may be >> detected by the F-test but, if they fall within a box, the H0 may not be >> rejected by the t-test. See http://www.amstat.org/publ >> ications/jse/v16n3/martin.html (Tom Nichols alerted me once to Fig. 2). >> It is a bit of a different plot than your example (because you are >> wondering about the discrepancy of positive detections) but it may be >> worthwhile to mention. >> Cheers, >> Andreas >> >> >> Von: FSL - FMRIB's Software Library <[log in to unmask]> on behalf of >> "Anderson M. Winkler" <[log in to unmask]> >> Antworten an: FSL - FMRIB's Software Library <[log in to unmask]> >> Datum: Samstag, 3. Dezember 2016 um 10:49 >> An: <[log in to unmask]> >> Betreff: Re: [FSL] Discrepancy between f- and t-test images >> >> Hi Lisa, >> >> Oops, my bad, it's Hayter, not Hayer: Hayter AAJ. The maximum familywise >> error rate of Fisher’s least significant difference test. J Am Stat Assoc. >> 1986 Dec;81(396):1000–4. http://www.jstor.org/stable/2289074 >> >> However you don't have to bother much with it -- it refers to differences >> more in the opposite direction, i.e., excess false positives as opposed to >> not finding results in the t-test, and also it shows that with 3 groups >> it's fine. The fact that you are using cluster-level inference already >> explains the issue: there is no guarantee that the F-test will match the >> t-tests even in the 3-group case. >> >> Which to choose then? I would go for the one that has higher specificity: >> the t-tests. I would leave the F-test results aside. >> >> All the best, >> >> Anderson >> >> >> On 2 December 2016 at 12:28, Lisa Kramarenko <[log in to unmask]> >> wrote: >> >>> Hi Anderson, >>> >>> thanks for your response! Indeed, I am comparing three groups and I am >>> using easythresh (after flameo) which performs multiple comparison >>> correction at the cluster level! >>> Unfortunately I can't find the paper you're referring to, could you also >>> tell me its name? Or maybe you can really briefly summarize what the reason >>> for this discrepancy is? >>> And I have another question: would you mind giving a hint about how to >>> interpret the not-matching results? Is it a difference to be reported or >>> rather not? >>> >>> Thanks so much for your help! >>> >>> >>> On 1 December 2016 at 10:16, Anderson M. Winkler <[log in to unmask] >>> > wrote: >>> >>>> Hi Lisa, >>>> >>>> The results may not match, particularly if: >>>> - Spatial statistics are used (e.g., cluster, TFCE). >>>> - The rank of the F-test diverges from 2 (e.g., if you are comparing 3 >>>> or more groups). For a reference, see Hayer (JASA, 1986). >>>> >>>> All the best, >>>> >>>> Anderson >>>> >>>> >>>> On 30 November 2016 at 10:26, Lisa Kr <[log in to unmask]> >>>> wrote: >>>> >>>>> Hello, >>>>> >>>>> I have some trouble understanding the discrepancy in the results of my >>>>> ANOVA. While the F-stat image shows the regions with significant >>>>> differences between my three groups, the individual t-tests then show that >>>>> the differences between the single groups are in regions other than these >>>>> F-test has shown (see attached, red=f-test, green and blue: group >>>>> differences). Is there any explanation for this? I was expecting the >>>>> differences between groups to fall in the general areas indicated by the >>>>> F-Test. >>>>> >>>>> Thanks!! >>>>> >>>>> Lisa >>>>> >>>>> >>>>> >>>> >>> >> >