Effects of restricted sampling on ITPA scaled scores

The Illinois Test of Psycholinguistic Abilities (ITPA) has received considerable attention as an instrument which can be used to assess and prescribe for individual learning problems. The ITPA was standardized on what was regarded as an "average" sample. One major criterion for determining "average" was an IQ between 84 and 116 on the abbreviated 1960 Stanford-Binet Intelligence Scale, Form L-M. In the present study, the effects of restricted sampling on the basis of IQ were examined, with the use of a simulation model. The results revealed that restricted sampling distorted certain derived scores, exaggerated mean dispersion scores, and made the analysis of individual profiles all but impossible. Restricted sampling was discussed in relation to the ITPA.