Re: Comparing two groups, small frequencies
From: Bruce Weaver (bweaver_at_lakeheadu.ca)
Date: 11/26/04
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Date: Fri, 26 Nov 2004 15:41:14 -0500
Marc Johansson wrote:
> Hi all,
>
> I'm trying to compare two groups that are not matched and observe a
> dependent variable with 3 different possible outcomes (ordinal, non
> gaussian). The total number of cases in outcome 1 and 2 are low. 2x3
> table looks like this:
> 1 1
> 0 3
> 20 27
>
> To compare both distributions, chi-square seems inappropriate because
> of the low observed frequencies in the first two rows. Mann-Whitney is
> not good because of many ties. Kolmogorov-Smirnov does not work
> because data is discrete instead of continuous. Is standard t testing
> acceptable despite strong deviation from gaussian distribution and low
> sample total (21 and 31 resp)? (expected normal distribution is all
> cases in outcome 3). What other test could I use?
>
> Many thanks in advance,
> Marc Johansson
>
I think StatXact has a generalization of the Fisher Exact test that
works for tables larger than 2x2. You could download the free 30-day
demo from www.cytel.com to check.
-- Bruce Weaver bweaver@lakeheadu.ca www.angelfire.com/wv/bwhomedir
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