Defining severe discrepancy in the diagnosis of learning disabilities: A comparison of methods

Given the significant increase in the number of students identified as learning-disabled (LD) and the growing concern about the overidentification of LD cases, attention has been focused on methods for determining a severe discrepancy between ability and achievement. Two such methods (a z-score discrepancy and a regression procedure) were compared by means of two different cutoff procedures on scores for 236 LD referrals. These results were then contrasted with a policy dictating that the lowest-achieving of those referred be considered as LD. Each student was evaluated with an individual intelligence scale and an achievement test. The results indicated that the regression procedure identified fewer students than did the z-score method. When the percentage of identified children is held constant, the methods were similar with respect to the types of errors made (false positives and false negatives). Data indicated that selecting the lowest-achieving students would have yielded about the same percentage of correct decisions, as defined by the multidisciplinary team, as did the two discrepancy methods. The policy implications of these findings are also considered.