Educational equity measurement: A comparative analysis of equity indicators

Accurate measurement is essential for realizing educational equity. This study examines four statistical indicators of equality of opportunity, a widely applied conceptualization of equity defined by the dependence of educational outcomes on predetermined circumstances. Four indicators (slope, R², concentration index [CI], and inequality of opportunity index [IOpI]) were compared using PISA 2018 data and simulation studies. Indicators yield divergent country rankings and contradictory equity assessments. These indicators also vary in their correlations with external criteria, with slope more weakly associated with human development and educational quality and IOpI more strongly linked to social inequality. Monte Carlo simulations demonstrate that IOpI and CI remain robust to both sample size reductions and measurement error in achievement scores in contrast to ESCS slope and R². These findings underscore that the choice of equity indicators is a consequential methodological decision with substantial implications for international comparison and domestic monitoring under the PISA operationalization.