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I am hoping for some advice regarding interpretation of Fishers exact test
output. I have some 3 x 2 contingency tables where the cell count is too small for a Chi-square to be computed. In the usual instance where the cell counts are large enough the residuals can be used to identify which associations are statistically significant. In the example that follows, Fishers exact test is employed, what criteria are used in in interpreting this reported significant association - e.g is the association just between group 3 and command.to.harm? command.to.harm group n y 1 97 7 2 28 5 3 16 7 p-value = 0.006 Any assistance with this enquiry is appreciated, regards Bob Green |
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At 10:19 AM 10/11/2006, Bob Green wrote:
>I am hoping for some advice regarding interpretation of Fishers exact test >output. > >I have some 3 x 2 contingency tables where the cell count is too small for >a Chi-square to be computed. In the usual instance where the cell counts >are large enough the residuals can be used to identify which associations >are statistically significant. In the example that follows, Fishers exact >test is employed, what criteria are used in in interpreting this reported >significant association - e.g is the association just between group 3 and >command.to.harm? > > >command.to.harm >group n y > 1 97 7 > 2 28 5 > 3 16 7 > > >p-value = 0.006 > > >Any assistance with this enquiry is appreciated, ... [show rest of quote] Was your p-value obtained with the special Fisher's Exact procedure that SPSS sells separately from the Basic module? If not, do groups 2 & 3 have enough in common that distinguishes them from group 1 to merit combination of groups 2 & 3? If so, you can combine them which will retain the significant contrast with Group 1 and at the same time eliminate the small cell expected values that you get with a 2x3. This will collapse the table to a 2x2 so that the Basic Module version of the Chi-square becomes available. Also, I'm a bit bothered by the wording of your question, "what criteria are used in in interpreting this reported significant association - e.g is the association just between group 3 and command.to.harm?" I don't think this is the correct way to frame the question. Remember that the flip side of the high percentage of "yes's" in Group 3 is the high percentage of "No's" in Group 1. They are two sides of the same coin. Bob Schacht Robert M. Schacht, Ph.D. <[hidden email]> Pacific Basin Rehabilitation Research & Training Center 1268 Young Street, Suite #204 Research Center, University of Hawaii Honolulu, HI 96814 |
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