Chapter One
1.3 Agreement Statistics
TUTORIAL IN BIOSTATISTICS
Kappa coefficients in medical research
Helena Chmura Kraemer, Vyjeyanthi S. Periyakoil and Art Noda
SUMMARY
Kappa coefficients are measures of correlation between categorical variables often used as reliability or
validity coefficients. We recapitulate development and definitions of the K (categories) by M (ratings)
kappas (K × M), discuss what they are well- or ill-designed to do, and summarize where kappas now
stand with regard to their application in medical research. The 2 × M (M [greater than or equal to] 2)
intraclass kappa seems the ideal measure of binary reliability; a 2 × 2 weighted kappa is an excellent choice, though
not a unique one, as a validity measure. For both the intraclass and weighted kappas, we address continuing problems
with kappas. There are serious problems with using the K × M intraclass (K > 2) or the various
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