>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
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'.