WAIS-IV subtest covariance structure: conceptual and statistical considerations

D. Wechsler (2008b) reported confirmatory factor analyses (CFAs) with standardization data (ages 16-69 years) for 10 core and 5 supplemental subtests from the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV). Analyses of the 15 subtests supported 4 hypothesized oblique factors (Verbal Comprehension, Working Memory, Perceptual Reasoning, and Processing Speed) but also revealed unexplained covariance between Block Design and Visual Puzzles (Perceptual Reasoning subtests). That covariance was not included in the final models. Instead, a path was added from Working Memory to Figure Weights (Perceptual Reasoning subtest) to improve fit and achieve a desired factor pattern. The present research with the same data (N = 1,800) showed that the path from Working Memory to Figure Weights increases the association between Working Memory and Matrix Reasoning. Specifying both paths improves model fit and largely eliminates unexplained covariance between Block Design and Visual Puzzles but with the undesirable consequence that Figure Weights and Matrix Reasoning are equally determined by Perceptual Reasoning and Working Memory. An alternative 4-factor model was proposed that explained theory-implied covariance between Block Design and Visual Puzzles and between Arithmetic and Figure Weights while maintaining compatibility with WAIS-IV Index structure. The proposed model compared favorably with a 5-factor model based on Cattell-Horn-Carroll theory. The present findings emphasize that covariance model comparisons should involve considerations of conceptual coherence and theoretical adherence in addition to statistical fit.     

Replication of the factor structure of the Wechsler Adult Intelligence Scale--Third Edition with a Canadian sample

Exploratory and confirmatory factor analyses of the subtests of the Wechsler Adult Intelligence Scale--Third Edition (WAIS-III; D. Wechsler, 1997b) were conducted on a stratified sample of Canadian adults (n = 718). As was previously demonstrated for the children's version of this scale, the factor model of the American standardization sample was replicated across this Canadian national sample. Results of the factor analyses confirmed the presence of the 4 WAIS-III factors: Verbal Comprehension, Perceptual Organization, Working Memory, and Processing Speed.     

Expanding the ecological validity of WAIS-IV and WMS-IV with the Texas functional living scale

Assessment of functional status is an important aspect of clinical evaluation. As part of the standardization of the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) and Wechsler Memory Scale-Fourth Edition (WMS-IV), participants completed the Texas Functional Living Scale (TFLS), a measure of Instrumental Activities of Daily Living. The relationships between TFLS and WAIS-IV and WMS-IV were examined in both normally developing and clinical samples. In general, the highest correlations were between TFLS and measures of general cognitive ability (WAIS-IV FSIQ [Full Scale IQ] and GAI [General Ability Index]) and working memory (WAIS-IV WMI [Working Memory Index] and WMS-IV VWMI [Visual Working Memory Index]). Across the clinical populations, working memory subtests were generally strongly related to TFLS performance, although this relationship was more consistent with WAIS-IV than WMS-IV. Contrast scaled scores are presented for the TFLS based on WAIS-IV or WMS-IV performance. These scores allow the evaluation of functional abilities within the context of cognitive and memory ability, enhancing and expanding the utility of the WAIS-IV and WMS-IV.     

Second-order confirmatory factor analysis of the WAIS-III. Wechsler Adult Intelligence Scale

According to Vernon's structure-of-intellect paradigm, abilities can be conceptualized as a hierarchy, with a factor of general intelligence at the top of the hierarchy, and successively more specific abilities toward the bottom. This paradigm has proven useful for interpreting a number of Wechsler intelligence scales. However, most of the research with this paradigm has used exploratory factor analysis, and the validity of the paradigm for the newest Wechsler Adult Intelligence Scale (WAIS-III) has yet to be evaluated. The present study examined the WAIS-III using second-order confirmatory factor analysis, which is a more appropriate analytic tool when specific hypotheses are tested. Using the standardization sample for the WAIS-III (N = 2,450), support was found for the hierarchical factor structure with a second-order factor of general intelligence and four first-order factors of Verbal Comprehension, Perceptual Organization, Working Memory, and Processing Speed.     

WISC-IV and WISC-III profiles in children with ADHD

Wechsler Intelligence Scale for Children, 3rd and 4th editions (WISC-III n = 586 and WISC-IV n = 118), profiles were compared for children with ADHD and normal intelligence. Mean Verbal Comprehension Index (VCI) and Perceptual Organization/Perceptual Reasoning Index (POI/PRI) scores were significantly higher than Freedom From Distractibility/Working Memory Index (FDI/WMI) and Processing Speed Index (PSI), and Symbol Search was higher than Coding. FDI/WMI and PSI scores were similar on both tests, but VCI and POI/PRI were higher on the WISC-IV than on the WISC-III. Therefore, index discrepancies were greater for the WISC-IV, suggesting that the WISC-IV might be better than the WISC-III in delineating the strengths and weaknesses of children with ADHD. All children in the WISC-IV sample scored lowest on WMI or PSI, whereas only 88% of the WISC-III children scored lowest on FDI or PSI. Thus, the WISC-IV may be more helpful in diagnosing ADHD than the WISC-III.     

A confirmatory factor analysis of the WISC-III in a clinical sample with cross-validation in the standardization sample.

Maximum likelihood confirmatory factor analysis was applied to the Wechsler Intelligence Scale for Children-Third Edition (WISC-III; Wechsler, 1991) data of a mixed clinical sample of 318 children. Analyses were designed to determine which of nine hypothesized oblique factor solutions could best explain intelligence as measured by the WISC-III in the clinical sample. Competing latent variable models were identified in previous studies, and results in the clinical sample were cross-validated by testing all models in the WISC-III standardization sample (n = 2200). Findings in both the clinical and standardization samples supported a five-factor model including Verbal Comprehension, Constructional Praxis, Visual Reasoning, Freedom from Distractibility, and Processing Speed factors. The Visual Reasoning factor was defined primarily by Picture Arrangement, whereas Mazes did not appear to improve model fit. Potential opportunities and pitfalls with regard to the interpretation of the proposed Visual Reasoning factor are discussed.     

Factor structure of the Norwegian version of the WAIS-III in a clinical sample: the arithmetic problem

Confirmatory Factor Analyses (CFA) of the Wechsler Adult Intelligence Scale-III (WAIS-III) lend partial support to the four-factor model proposed in the test manual. However, the Arithmetic subtest has been especially difficult to allocate to one factor. Using the new Norwegian WAIS-III version, we tested factor models differing in the number of factors and in the placement of the Arithmetic subtest in a mixed clinical sample (n = 272). Only the four-factor solutions had adequate goodness-of-fit values. Allowing Arithmetic to load on both the Verbal Comprehension and Working Memory factors provided a more parsimonious solution compared to considering the subtest only as a measure of Working Memory. Effects of education were particularly high for both the Verbal Comprehension tests and Arithmetic.     

Seemingly Anomalous WISC-IV Full Scale IQ Scores in the American and Canadian Standardization Samples

The American and Canadian standardization samples for the fourth edition of the Wechsler Intelligence Scale for Children were used to ascertain the prevalence of “seemingly anomalous” Full Scale IQ (FSIQ) scores for all possible sums of scaled scores combinations of the Verbal Comprehension Index, Perceptual Reasoning Index, Working Memory Index, and Processing Speed Index. About 1% of FSIQ scores in both samples were anomalous (that is, fell outside the range of the four indices). Interestingly, the prevalence of anomalous scores was higher at the extremes of the FSIQ distribution. Moreover, anomalous FSIQ scores occurring above or below the mean of the FSIQ distribution (that is, 100) were larger or smaller, respectively, than any of the four indices. Furthermore, if the range of the four indices did contain the FSIQ (the non-anomalous case), when the FSIQ was below or above 100 it tended to be located distally in the half-segment of the range furthest below or above 100, respectively. A non-technical intuitive analogy from Olympic sports and a statistical explanation for the findings are provided. Important implications for practitioners are also presented. Portions of this paper were presented March 17, 2006 at the 20th annual Joseph R. Royce Research Conference, Department of Psychology, University of Alberta, Edmonton, Alberta.     

Seemingly Anomalous WISC-IV Full Scale IQ Scores in the American and Canadian Standardization Samples

The American and Canadian standardization samples for the fourth edition of the Wechsler Intelligence Scale for Children were used to ascertain the prevalence of “seemingly anomalous” Full Scale IQ (FSIQ) scores for all possible sums of scaled scores combinations of the Verbal Comprehension Index, Perceptual Reasoning Index, Working Memory Index, and Processing Speed Index. About 1% of FSIQ scores in both samples were anomalous (that is, fell outside the range of the four indices). Interestingly, the prevalence of anomalous scores was higher at the extremes of the FSIQ distribution. Moreover, anomalous FSIQ scores occurring above or below the mean of the FSIQ distribution (that is, 100) were larger or smaller, respectively, than any of the four indices. Furthermore, if the range of the four indices did contain the FSIQ (the non-anomalous case), when the FSIQ was below or above 100 it tended to be located distally in the half-segment of the range furthest below or above 100, respectively. A non-technical intuitive analogy from Olympic sports and a statistical explanation for the findings are provided. Important implications for practitioners are also presented. Portions of this paper were presented March 17, 2006 at the 20th annual Joseph R. Royce Research Conference, Department of Psychology, University of Alberta, Edmonton, Alberta.     

Generalizability of WISC-IV index and subtest score profiles in children with traumatic brain injury

The Wechsler Intelligence Scale for Children, 4th edition (WISC-IV) is often used to assess children with traumatic brain injury (TBI); although limited information is available regarding its psychometric properties in these children. Two recent reports suggest that the Perceptual Reasoning Index is not uniquely sensitive to TBI, which differs from the Perceptual Organization Index of the WISC-III. The current study examined WISC-IV profiles in two independently gathered samples of children with TBI. Examination of profiles indicated similarities between the current findings and those reported in other studies, in that the greatest deficits were present on the Processing Speed Index and its component subtests of Coding and Symbol Search, while the Perceptual Reasoning index score was comparable to the Verbal Comprehension Index. Also, no significant index or subtest score differences were present when the current sample was compared to the children with TBI reported by Allen, Thaler, Donohue and Mayfield (2010 ). The present findings are consistent with two prior studies of the WISC-IV in children with TBI, providing additional evidence for profile differences between the WISC-III and WISC-IV. The results also suggest that WISC-IV profiles reported in prior studies are generalizable across TBI samples and study sites.     

Advanced clinical interpretation of the WAIS-IV and WMS-IV: prevalence of low scores varies by level of intelligence and years of education

Clinicians can use the base rates of low scores in healthy people to reduce the likelihood of misdiagnosing cognitive impairment. In the present study, base rates were developed for the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) and Wechsler Memory Scale-Fourth Edition (WMS-IV) using 900 healthy adults and validated on 28 patients with moderate or severe traumatic brain injuries (TBIs). Results indicated that healthy people obtain some low scores on the WAIS-IV/WMS-IV, with prevalence rates increasing with fewer years of education and lower predicted intelligence. When applying the base rates information to the clinical sample, the TBI patients were 13 times more likely to be identified as having a low cognitive profile compared with the controls. Using the base rates information is a psychometrically advanced method for establishing criteria to determine low cognitive abilities on the WAIS-IV/WMS-IV.     

Estimation of Wechsler Adult Intelligence Scale-III index scores with the 7-subtest short form in a clinical sample

A 7-subtest short form of the Wechsler Adult Intelligence Scale-III (WAIS-III) previously demonstrated good comparability in estimating Full Scale and Verbal IQ summary scores, with adequate comparability in estimating Performance IQ. In a mixed clinical sample of 295 patients, the current study assessed the equivalence of the index scores generated from the full and prorated WAIS-III. The results revealed correlations corrected for redundancy of .90, .86, .87, and .75 for the Verbal Comprehension (VCI), Perceptual Organization (POI), Working Memory (WMI), and Processing Speed (PSI) indexes, respectively. Although the 7-subtest short form of the WAIS-III was not designed to estimate index scores, adequate estimates are viable for VCI, POI, and WMI when the goal is to obtain group, rather than individual, data points.     

The effects of Wechsler Intelligence Scale for Children-Fourth Edition cognitive abilities on math achievement

This study used structural equation modeling to examine the effect of Stratum III (i.e., general intelligence) and Stratum II (i.e., Comprehension-Knowledge, Fluid Reasoning, Short-Term Memory, Processing Speed, and Visual Processing) factors of the Cattell-Horn-Carroll (CHC) cognitive abilities, as operationalized by the Wechsler Intelligence Scale for Children, Fourth Edition (WISC-IV; Wechsler, 2003a) subtests, on Quantitative Knowledge, as operationalized by the Wechsler Individual Achievement Test, Second Edition (WIAT-II; Wechsler, 2002) subtests. Participants came from the WISC-IV/WIAT-II linking sample (n=550). We compared models that predicted Quantitative Knowledge using only Stratum III factors, only Stratum II factors, and both Stratum III and Stratum II factors. Results indicated that the model with only the Stratum III factor predicting Quantitative Knowledge best fit the data.     

Validity of a short form of the WISC-III in children with traumatic head injury

The concurrent, construct, and criterion validities of Donders' (in press) short form of the Wechsler Intelligence Scale for Children - Third Edition (WISC-III) were evaluated in a sample of 171 children with traumatic head injury (THI). Correlations between the short-form deviation quotients and their full-length counterparts were statistically significant. Confirmatory factor analysis revealed that a four-factor model (composed of Verbal Comprehension, Perceptual Organization, Freedom from Distractibility, and Processing Speed) fit the data relatively well. The short-form deviation quotients also had statistically significant correlations with length of coma. It is concluded that this short form is an accurate and valid alternative to the full-length WISC-III in children with THI.     

Factor analysis of the Wechsler adult intelligence scale-revised (WAIS-R): An examination of the standardization sample

Orthogonal and oblique factor analyses were performed using the Wechsler Adult Intelligence Scale-Revised (WAIS-R) standardization sample (Wechsler, 1981). Using objective criteria, it was decided to retain two factors. Evidence for a strong general intelligence (g) factor was found from both the orthogonal and oblique rotations. Whereas the verbal IQ provided an acceptable estimate of the Verbal Comprehension factor, a purer measure was found in the form of a Verbal Comprehension Deviation Quotient containing only the Information, Vocabulary, Comprehension, and Similarities subtests. The performance IQ was found to be an inadequate measure of the Perceptual Organization factor. A Perceptual Organization Deviation Quotient, containing only the Block Design and Object Assembly subtests, was recommended as an effective alternative. Analysis of the variance components for each subtest at every age level revealed that a substantial proportion of subtests at a wide range of age levels evidence either high or intermediate levels of specific variance. These results are discussed in terms of interpreting individual subtest scores and patterns. Each of the study's major findings are compared with prior work done with the Wechsler Adult Intelligence Scale (WAIS) (Wechsler, 1955).     

Confirmatory factor analyses of the WAIS-III standardization data

Confirmatory factor analyses with the standardization data of the Wechsler Adult Intelligence Scale-Third Edition (Wechsler, 1997a) compared 6 models with 1 to 4 factors for 11- and 13-subtest versions of the test. Three factors usually fit the data better than 2 factors, but 2-factor models were more parsimonious. A 2-factor model with a Verbal Comprehension factor (Vocabulary, Similarities, Information, and Comprehension) was as good as and sometimes better than the 2-factor model defined by the traditional separation of Verbal and Performance subtests. For 3-factor models, alternative specifications of processing speed subtests on either the Perceptual Organization or Freedom From Distractibility factor were comparable, and specifying a 4th factor for Digit Symbol and Symbol Search had little advantage in comparison with 3-factor models with correlated errors for the 2 subtests.     

Construct and concurrent validity of the Cambridge neuropsychological automated tests in Portuguese older adults without neuropsychiatric diagnoses and with Alzheimer’s disease dementia

We aimed to analyze the construct and concurrent validity of the Rapid Visual Information Processing (RVP), Paired Associates Learning (PAL), Reaction Time (RTI), and Spatial Working Memory (SWM) tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB®). Inclusion criteria were checked in a first session. The CANTAB and additional pencil-and-paper tests were administered within 1 week. The participants (aged 69–96 years) were 137 Portuguese adults without neuropsychiatric diagnoses and 37 adults with mild-to-moderate Alzheimer’s disease dementia. Comparisons were made between the CANTAB tests and between these tests and the Rey Complex Figure Test (RCFT), Verbal Fluency (VF) test, and some Wechsler Memory Scale-III and Wechsler Adult Intelligence Scale-III subtests. Most intra-test correlations were stronger than the CANTAB inter-test correlations. The RVP correlated more with VF animals (.44), the PAL with RCFT immediate recall (–.52), the RTI with RVP mean latency (.42), and the SWM with Spatial Span backward (–.39).     

The WISC-V in children and adolescents with epilepsy

Despite its popularity in the neuropsychological evaluation of children, the utility of the Wechsler Intelligence Scale for Children – Fifth Edition (WISC-V) has not yet been investigated in children with epilepsy. Eighty clinically referred children and adolescents with epilepsy were administered the WISC-V as part of a comprehensive assessment and scores were compared to matched controls from the WISC-V standardization sample. T tests compared WISC-V indices and subtests between patients and controls and Chi-square analyses compared the rates of low scores. Correlational analyses assessed the relationships between epilepsy severity variables (e.g., age of onset, duration of epilepsy, number of antiepileptic drugs, seizure frequency). All WISC-V composites and subtests were significantly lower in patients versus controls and the rate of low scores was higher in patients than controls for all composites and subtests with the exception of Figure Weights. The Working Memory Index and Processing Speed Index were most sensitive to impairment, while the Verbal Comprehension Index and Fluid Reasoning Index were least sensitive. Of the epilepsy severity variables, age of seizure onset and number of antiepileptic drugs were strong predictors of deficits, whereas seizure frequency was the weakest predictor. Importantly, no significant differences were seen in children with right hemisphere epilepsy versus left on the five WISC-V composites, though a trend was seen towards a lower Visual-Spatial Index in those with right-sided focal seizures.     

Two- and three-factor solutions of the WAIS-III

The third edition of the Wechsler Adult Intelligence Scale manual reports four-factor solutions for the WAIS-III, and subsequent research has validated four-factor solutions for a variety of samples. These four factors consistently correspond to the four Factor Indexes that are yielded by the WAIS-III. However, the WAIS-III still provides Verbal and Performance IQs, in addition to the Indexes, making it desirable to examine two-factor solutions as well. In addition, because the Wechsler literature includes much interpretation of three-factor solutions, these solutions were likewise examined. Principal factor analysis followed by Varimax and Oblimin rotations of two and three factors were performed on data for the total WAIS-III sample ages 16 to 89 years (N=2,450). The two-factor solutions were viewed as a construct validation of Wechsler's two separate IQs, although the Working Memory subtests tended to load higher on the Performance scale than on their intended scale (Verbal); three-factor solutions were interpreted within the context of Horn's expanded fluid-crystallized theory and research on working memory. Both the two- and three-factor Varimax-rotated solutions were related to similar factor analyses conducted previously for the Wechsler Adult Intelligence Scale-Revised and the Wechsler Intelligence Scale for Children-III. Coefficients of congruence between like-named factors consistently exceeded .90, and usually .98, across different Wechsler batteries.     

Individual differences in false memory from misinformation: Cognitive factors

This research investigated the cognitive correlates of false memories that are induced by the misinformation paradigm. A large sample of Chinese college students (N=436) participated in a misinformation procedure and also took a battery of cognitive tests. Results revealed sizable and systematic individual differences in false memory arising from exposure to misinformation. False memories were significantly and negatively correlated with measures of intelligence (measured with Raven's Advanced Progressive Matrices and Wechsler Adult Intelligence Scale), perception (Motor-Free Visual Perception Test, Change Blindness, and Tone Discrimination), memory (Wechsler Memory Scales and 2-back Working Memory tasks), and face judgement (Face Recognition and Facial Expression Recognition). These findings suggest that people with relatively low intelligence and poor perceptual abilities might be more susceptible to the misinformation effect.