The unitary ability of IQ and indexes in WAIS-IV

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

Intelligence and working memory control: Evidence from the WISC-IV administration to Italian children

Working memory (WM) has been associated with general intelligence (GI). However, evidence is contradictory, as the relationship has in some cases resulted to be very high, and in other cases very low. To explain these differences, it has been argued that WM is an articulated system and only its more attentional components are strictly related with GI. In particular, it has been argued that WM tasks can be located – according to the task characteristics and the subject's age – along a continuum, from the most passive tasks, which do not require cognitive control, to the most active tasks, which do require high cognitive control. The present study tested this hypothesis using data collected during the standardization of the Italian version of the WISC-IV. WISC-IV, includes four measures, i.e. the arithmetic test, the letter-number sequencing test, the backward and the forward digit span tests, which represent decreasing levels of cognitive control. The analysis of correlations between the four tasks and a measure of GI – obtained with the six basic tasks (related to verbal comprehension and perceptual reasoning, but not to working memory) – confirmed the hypothesis and showed that the pattern of correlations only slightly changes across ages

Differences in the intellectual profile of children with intellectual vs. learning disability.

The WISC-IV was used to compare the intellectual profile of two groups of children, one with specific learning disorders (SLDs), the other with intellectual disabilities (ID), with a view to identifying which of the four main factor indexes and two additional indexes can distinguish between the groups. We collected information on WISC-IV scores for 267 children (Mage=10.61 [SD=2.51], range 6-16 years, females=99) with a diagnosis of either SLD or ID. Children with SLD performed better than those with ID in all measures. Only the SLD children, not the ID children, revealed significant differences in the four main factor indexes, and their scores for the additional General Ability Index (GAI) were higher than for the Cognitive Proficiency Index (CPI). Children with a diagnosis of SLD whose Full-Scale Intelligence Quotient (FSIQ) was <85 showed a similar pattern. Our findings confirm the hypothesis that children with SLD generally obtain high GAI scores, but have specific deficiencies relating to working memory and processing speed, whereas children with ID have a general intellectual impairment. These findings have important diagnostic and clinical implications and should be considered when making diagnostic decisions in borderline cognitive cases

Corsi's block-tapping test: standardization and concurrent validity with WISC-R for children aged 11 to 16.

Corsi's block-tapping test and WISC-R were given to 1122 children from 11 to 16 years of age. Corsi's raw scores were transformed into standard scores like those for the WISC-R subtests. Reliabilities, standard score equivalents of raw scores, correlations with scores on WISC-R subtests, scales and factor scores are presented. A Principal Factor analysis of intercorrelations for Corsi's test and WISC-R subtests shows a three-factor solution with Corsi's test loading on the Third Factor. Results agree with Wielkiewicz's (1990) hypothesis about the construct underlying WISC-R Third Factor as "executive" and short-term memory processes