Chronological age and Peabody Picture Vocabulary Test performance of persons with mental retardation: new data.

The Test de Vocabulaire en Images (the French version of the Peabody Picture Vocabulary Test) and the Columbia Mental Maturity Scale were administered to 44 persons with mental retardation who were aged 6.8 yr. to 18.2 yr. Analysis indicated a significant influence of chronological age on the Test de Vocabulaire en Images Mental Age. This influence of chronological age probably explains why receptive vocabulary tests consistently overestimate the IQ of persons with mental retardation.