Illusory coerrelations in school psychologists\u27 diagnoses of learning disabilities

Illusory correlation is the perception of an association between two uncorrected variables such as intersubtest scatter on the Wechsler Intelligence Scale for Children - Third Edition (WISC-III) and the presence of a learning disability. This study assessed the extent to which school psychologists are influenced by this illusory correlation. Three independent variables were varied systematically. One variable was relevant to the diagnosis of a learning disability (a discrepancy between expected and actual levels of achievement on the Wechsler Individual Achievement Test (WIAT)). Another was irrelevant to the diagnosis (intersubtest scatter on the WISC-III). The third independent variable was used as a warning to those participants who had an illusory belief that intersubtest scatter on the WISC-III is a valid indicator of a learning disability. Certified school psychologists randomly received case study material for a child referred for a psychological evaluation. It was found that participants based their diagnostic decisions about learning disabilities on the illusory belief that intersubtest scatter on the WISC-III is a valid indicator of a learning disability in the no warning condition only. When warned of this illusory belief, this effect disappeared. This illusory belief, therefore, could effect school psychologists\u27 diagnostic decisions and therefore falsely identify children as learning disabled