st: Re: Fisher's exact test in r x c contingency tables

[Roger Newson <roger.newson@kcl.ac.uk>]

At 17:16 02/06/2005, Mike Lacy wrote (amongst other useful stuff):

> >What is your opinion? At the moment I rather think about applying
> >tests that were designed for ordinal / ordinal relationships in r x c
> >contingency tables (say, Goodman and Kruskal's gamma) than
> >embarking on a potentially hazardous procedure.
>
> If your variables are nominal, gamma would not make sense.  However, if 
> your variables are actually ordered but your data are sparse, you might 
> want to bootstrap the Gamma value:
>
> bootstrap r(gamma), reps(1000) : tabulate rep78 pricecat, gamma
Alternatives to Kruskal's gamma include Somers' D and Kendall's tau-a, 
which can be estimated with confidence intervals using the -somersd- 
package (downloadable from SSC). More about the case for confidence 
intervals for Somers' D and Kendall's tau-a can be found in Newson (2002), 
of which you can download a preprint from my website (see my signature below).

Hope this helps.

Roger


References

Newson R. 2002. Parameters behind "nonparametric" statistics: Kendall's 
tau, Somers' D and median differences. The Stata Journal 2(1): 45-64.


--
Roger Newson
Lecturer in Medical Statistics
Department of Public Health Sciences
Division of Asthma, Allergy and Lung Biology
King's College London

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Tel: 020 7848 6648 International +44 20 7848 6648
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Email: roger.newson@kcl.ac.uk
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Opinions expressed are those of the author, not the institution.

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