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,
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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