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Date:   Fri, 20 Apr 2007 14:06:35 -0400
Reply-To:   Peter Flom <peterflomconsulting@mindspring.com>
Sender:   "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:   Peter Flom <peterflomconsulting@MINDSPRING.COM>
Subject:   Re: Kendall coefficient of concordance
Comments:   To: Michelle Secic <consult@SECICSTATS.COM>
Content-Type:   text/plain; charset=UTF-8

>From: Michelle Secic <consult@SECICSTATS.COM> wrote >I'm looking at concordance of two raters on 3 possible findings and the 3 >x 3 crosstable of the findings have lots of zeros and the Kendall stat via >%magree results in 0.5 even though almost all the data (n>250) fall in a >single cell of agreement. Please let me know if you know of any >references that talk about unreliabile Kendell stat with lots of zeros, or >something like that. I'm trying to find a reference for this... Thanks >so much!!!

Kendall's coefficient isn't unreliable, it just answers one particular question. If you want to aks a different question, then you want a different statistic. There are a vast number of statistics to measure agreement between raters, most notably Cohen's kappa: http://en.wikipedia.org/wiki/Cohen's_kappa

This, and many other measures, are discussed in many books on nonparametric statistics. e.g.

Agresti: Categorical Data Analysis Fleiss: Statistical Methods for Rates and Proportions

You can also search Lex Jansen's page: http://www.lexjansen.com/sugi/ for keywords like 'agreement'.

HTH

Peter


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