Quantifying a severe discrepancy: A critical analysis. Learning Disability Quarterly

Abstract. The four basic methods of quantifying severe academic discrepancy grade level deviation, expectancy formula, standard-score comparisons, and regression analysis-are evaluated in terms of: ease of administration, measure-ment errors, regression effects, years in school, changes in variation of achieve-ment scores at different grades, comparability of norms, incidence, and systematic and consistent treatment of IQ/achievement interrelationship. Results indicate that both the deviation from grade level and the expectancy formulas fail to con-sider almost all critical variables. While the IQ/standard-score method takes into account several of the factors, it does not adequately consider regression effects. The a priori analysis indicates that the regression equation approach considers almost all the criterion variables with the exception of years in school. Hence based upon critical statistical and measurement concepts, the authors tentatively conclude that the latter approach is superior to the other quantification methods analyzed. It is emphasized, however, that such aspects as incidence and student characteristics can only be empirically determined