The unitary ability of IQ and indexes in WAIS-IV

Orsini, A., Pezzuti, L. and Hulbert, S. (2015) The unitary ability of IQ and indexes in WAIS-IV. European Journal of Psychological Assessment. ISSN 1015-5759.


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Lichtenberger and Kaufman (2009, p. 167) defined unitary ability as ‘an ability […] that is represented by a cohesive set of scaled scores, each reflecting slightly different or unique aspects of the ability’. Flanagan and Kaufman (2009) and Lichtenberger and Kaufman (2012) used a difference of 23 IQ points between the highest score (Max) and the lowest score (Min) obtained by a subject in the four Indexes of the WAIS-IV to define unitarity of the total IQ score. A similar method has been used to assess the unitary ability of the four Indexes, with a threshold of 5 points. Such difference scores (of 23 for IQ and 5 for Indexes) are considered high and infrequent and the authors therefore conclude that the corresponding Full-Scale IQ score or Index score is uninterpretable. In this paper we argue that these thresholds are inappropriate because they are based on the wrong standard deviation. The main aim of this study was to establish variability thresholds for IQ and the WAIS-IV Indexes for the American standardization sample and to compare these thresholds with those for the Italian standardization sample. We also consider an alternative approach to determining whether an IQ score represents a unitary ability, based on the maximum difference score for the 10 core subtests that contribute to Full-Scale IQ scores.

Item Type: Article
Additional Information: "This article does not exactly replicate the final version published in the journal European Journal of Psychological Assessment. It is not a copy of the original published article and is not suitable for citation."
Subjects: B Philosophy. Psychology. Religion > BF Psychology > BF0712 Developmental psychology
R Medicine > RC Internal medicine > RC0435 Psychiatry > RC0467 Clinical psychology
Divisions: Faculty of Social and Applied Sciences > School of Psychology, Politics and Sociology
Depositing User: Dr Sabina Hulbert
Date Deposited: 22 Jul 2015 11:40
Last Modified: 24 Dec 2016 18:25

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Last edited: 29/06/2016 12:23:00