A Comparison of Gwet’s AC1 and Kappa When Calculating Inter-Rater Reliability Coefficients in a Teacher Evaluation Context

With increased emphasis on teacher quality in the Race to the Top federal grants program, rater agreement is an important topic in teacher evaluation. Variations of kappa have often been used to assess inter-rater reliability (IRR). Research has shown that kappa suffers from a paradox where high exact agreement can produce low kappa values. Two chance-corrected methods of IRR were examined to determine if Gwet’s AC1 statistic is a more stable estimate than kappa. Findings suggest that Gwet’s AC1 statistic outperforms kappa as a chance-corrected measure of IRR when compared to exact agreement. Findings suggest Gwet’s AC1 statistic shows promise for future IRR studies in a teacher evaluation context.