RELATIVE IMPROVEMENT OVER CHANCE (RIOC) FOR 2X2 TABLES

A novel index of association, called Relative Improvement Over Chance (RIOC), is described for 2×2 tables that corrects for chance and for limitations in maximum predictability due to unequal distributions of the marginals in such tables. Criteria for comparing the utility of this and existing indexes of association are reviewed. The theoretical distribution of RIOC for large and small sample sizes is presented, and tested against the results from computer generated tables. Methods are presented for calculating confidence intervals for RIOC, for testing the significance of individual values of RIOC, and for testing the difference between several values of RIOC from different studies. 1990 The British Psychological Society