Floor effects on the WISC-IV

Seventeen 16-year-olds in special education were given both the Wechsler Adult Intelligence Scale (WAIS)-III and the Wechsler Intelligence Scale for Children (WISC)-IV in counterbalanced order. It was found that there was a significant floor effect on the WISC-IV due to low raw scores and raw scores of 0 being given a scaled score of 1. Extrapolating the relationship between raw scores and scaled scores down below raw score, one showed that the WISC-IV may be overestimating some low intelligence quotients (IQs) by several IQ point due to this floor effect.