On 2 Jun 2001, Bekir wrote in part:
> I performed a study on " different enteral nutrients and bacterial
> translocation in experimental obstructive jaundice."
>
> There was 5 groups of rats. Each group consists of 20 rats. Occurred
> Translocation incidences in mesenteric lymph nodes were shown in
> following table. My aim was to compare groups 2, 3, 4 with
> control(group 1)
< Data table deleted; see the original posting. >
< Summary of group definitions and comparison results:
> Group 1 sham ligation of bile duct (fed rat chow)
> Group 2 bile duct ligated (fed rat chow) * p = 0.08
> Group 3 bile duct ligated (fed enteral diet) ** p = 0.02
> Group 4 bile duct ligated (fed enteral diet 2)
> Group 5 bile duct ligated (fed enteral diet 3)
> By chi squared test I calculated this p values.
You did not specify, but presumably the chi-square test in question was
of a series of 2x2 tables, comparing the numbers of translocations that
occurred (vs. the numbers that didn't) in Group 1 (your control group)
with each of the other groups.
> The reviewer commented that I should do bonferroni correction, find
> adjusted p value and according to this adjusted value, I should say
> significant or not. However, in no study have I read that the authors
> had written that they had adjusted bonferroni correction, especially
> in a comparision by chi square test.
The 1-degree-of-freedom chi-square test described above is exactly
equivalent to a z-test comparing the proportion of translocations in
Group 1 with the proportion of translocations in the other group, for
each conmparison of interest. You may perhaps find references to
Bonferroni adjustments in studies where z- or t-tests were used.
> If bonferroni was performed then adjusted p value
[Here you must mean the adjusted significance level alpha,
not the p-value? -- DFB.]
> would be 0.05/10=0.005, 10 = nx(n-1) in our study.
I do not think so. The number of comparisons you say you were
interested in is three, not ten:
Group 2 vs. Group 1, Group 3 vs. Group 1, and Group 4 vs. Group 1.
If indeed these are the only comparisons of interest, and in the sense
that these comparisons (and no others!) were planned from the beginning,
then the adjusted p-values would be 0.02*3 = 0.06 and 0.008*3 = 0.024.
But I do not believe this, either. If these were the only three
comparisons of interest, you would not have bothered to include Group 5
in the experiment. It looks to me as though the original design had
envisioned comparisons of Groups 2, 3, 4, 5 vs. Group 1, and may also
have intended comparisons of Groups 3, 4, 5 vs. Group 2; so that the
number of comparisons for the Bonferroni correction would be either 4,
or 4+3 = 7. The corresponding adjusted p-values would be 0.02*4 = 0.08
and 0.008*4 = 0.032; or 0.02*7 = 0.14 and 0.008*7 = 0.056.
> Thus our results would not be significant.
> Is it appropriate to make bonferroni correction or simes correction in
> this situation?
> Indeed I want to compare groups 2, 3, 4 with group 1. So there would
> be 4 comparisons.
Then you must mean "compare groups 2, 3, 4, 5 with group 1"?
> Is simes procedure is correct? How can I make Simes correction?
Sorry, I'm not familiar with this procedure, at least not by that name.
I hope this has been helpful.
------------------------------------------------------------------------
Donald F. Burrill [EMAIL PROTECTED]
348 Hyde Hall, Plymouth State College, [EMAIL PROTECTED]
MSC #29, Plymouth, NH 03264 603-535-2597
184 Nashua Road, Bedford, NH 03110 603-471-7128
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