WISC-IV and intellectual disability: The use of age equivalent [WISC-IV e disabilità intellettiva L'uso dell'età equivalente]

The WISC-IV is the most used battery for the assessment of intelligence in children. When used on individuals with intellectual disability, it may hit a floor effect. This implies an overestimation of total IQ and a flattening of the profile. Floor effect is a serious problem when IQ < 50. Two proposed methods to avoid floor effect are the z scores and equivalent age instead of the traditional scaled scores. The present study examines the pros and cons of using equivalent age (rather than z scores) to define the intellectual profile and level of children with intellectual disability, especially in severe cases. It also proposes an extrapolation of the equivalent ages below 6 years (not available from the WISC-IV manual)