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Date:         Mon, 26 Aug 2002 15:12:39 -0700
Reply-To:     Cassell.David@EPAMAIL.EPA.GOV
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "David L. Cassell" <Cassell.David@EPAMAIL.EPA.GOV>
Subject:      Re: Stratified Non-parametric analysis / confidence intervals
Content-type: text/plain; charset=us-ascii

Jones John <John.Jones@UCB-GROUP.COM> replied: > I would recommend some variation on the Cochran-Mantel-Hanzel test. This > statistic is well documented in the FREQ procedure.

While I agree with John's excellent (of course!) advice, I just want to point out one issue. The original poster wrote:

>> The van Elteren test could be an alternative, but according to a text >> book, it is only applicable, if the results per center are not >> contradicting each other (i.e., in one center treatment A is better than >> B and in an other center B is better than A).

The CMH tests also are at a disadvantage when the results by 'stratum' are not all aligned similarly. In fact, CMH tests are notorious for their low power for detecting a significant association when the patterns for some strata run opposite to those of other strata. So the poster needs to check for this when reporting his results, because a nonsigificant result *may* mean that no association was found, or it *may* mean that there is no dominant pattern of association, while significant associations can still exist within separate strata.

Ahh, the joys of real data...

David -- David Cassell, CSC Senior computing specialist mathematical statistician

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