The unitary ability of IQ in the WISC-IV and its computation.

Flanagan and Kaufman (2009) use a difference of 23 IQ points between the highest score (Max) and the lowest score (Min) reported by subjects in the 4 Indexes of Verbal Comprehension, Perceptual Reasoning, Working Memory and Processing Speed to define unitarity of IQ in the WISC-IV. Such a difference in scores is considered very rare and the authors therefore conclude that the total IQ scores in these cases cannot be interpreted. Hereby, we want to argue against the choice of this cut-off threshold value by showing that it was based on the wrong standard deviation value when first computed. [ABSTRACT FROM AUTHOR]