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!!!