Abstract
Various statistics have been proposed as standard methods for calculating and reporting interobserver agreement scores. The advantages and disadvantages of each have been discussed in this journal recently but without resolution. A formula is presented that combines separate measures of occurrence and nonoccurrence percentages of agreement, with weight assigned to each measure, varying according to the observed rate of behavior. This formula, which is a modification of a formula proposed by Clement (1976), appears to reduce distortions due to "chance" agreement encountered with very high or low observed rates of behavior while maintaining the mathematical and conceptual simplicity of the conventional method for calculating occurrence and nonoccurrence agreement.