Agreement or association: choosing a measure of reliability for nominal data in the 2 x 2 case--a comparison of phi, kappa, and G.
This research note compares the phi, kappa, and G measures of association and agreement used to estimate the reliability of drug and alcohol self-report data in the 2 x 2 case. Attention is focused upon the problems encountered in using these measures when skewed marginal distributions are found in a test-retest situation. The G index of agreement was found to be a stable estimator, unaffected by skewed marginals, and equivalent to kappa and phi when marginal distributions are equal.
D003625:Data Collection / Q000379:methods*; D006801:Humans; D012650:Self Disclosure; D013223:Statistics as Topic; D019966:Substance-Related Disorders; D011795:Surveys and Questionnaires