kappa simple chance-corrected agreement coefficient A Kappa statistic in which the expected agreement by chance is based on an assumption that all possible categories for assignment are equally likely. A Kappa statistic is a measure of agreement among categorical assessments, corrected for chance agreement. In the simple chance-corrected agreement coefficient, the expected chance agreement is modeled as the inverse of the number of categories (1/q) where q is the number of possible categories for assignment. The simple chance-corrected agreement coefficient is calculated as ( p[a] - 1/q ) / ( 1 - 1/q ) where p[a] is the observed percent agreement and q is the number of possible categories for assignment. Brian S. Alper, Harold Lehmann, Joanne Dehnbostel, Muhammad Afzal, Kenneth Wilkins https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5965565 Gwet KL. Testing the Difference of Correlated Agreement Coefficients for Statistical Significance. Educ Psychol Meas. 2016 Aug;76(4):609-637. doi: 10.1177/0013164415596420. Epub 2015 Jul 28. PMID: 29795880; PMCID: PMC5965565. Brennan and Prediger (1981) proposed a simple chance-corrected agreement coefficient, which generalizes to multiple raters and multiple categories, the G-index previously proposed by Holley and Guilford (1964) for two raters and two categories. What is known as the Holley–Guilford G-index was previously proposed independently by various authors under different names. Among them are Guttman (1945), Bennett, Alpert, and Goldstein (1954), and Maxwell (1977). For an interrater reliability experiment involving r raters who classify n subjects into one of q possible categories, the Brennan-Prediger coefficient is given by k[BP] = ( p[a] - 1/q ) / ( 1 - 1/q ), where the percent agreement p[a] is defined by Equation (3 -- see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5965565/#disp-formula3-0013164415596420), and the percent chance agreement is a constant representing the inverse of the number of categories. ready for release