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.     

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.     

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.     

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.     

Confirmatory factor analysis of the WAIS-IV/WMS-IV

The Wechsler Adult Intelligence Scale-fourth edition (WAIS-IV) and the Wechsler Memory Scale-fourth edition (WMS-IV) were co-developed to be used individually or as a combined battery of tests. The independent factor structure of each of the tests has been identified; however, the combined factor structure has yet to be determined. Confirmatory factor analysis was applied to the WAIS-IV/WMS-IV Adult battery (i.e., age 16-69 years) co-norming sample (n = 900) to test 13 measurement models. The results indicated that two models fit the data equally well. One model is a seven-factor solution without a hierarchical general ability factor: Verbal Comprehension, Perceptual Reasoning, Processing Speed, Auditory Working Memory, Visual Working Memory, Auditory Memory, and Visual Memory. The second model is a five-factor model composed of Verbal Comprehension, Perceptual Reasoning, Processing Speed, Working Memory, and Memory with a hierarchical general ability factor. Interpretative implications for each model are discussed.     

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.     

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).     

Loss of Financial Capacity in Alzheimer's Disease: The Role of Working Memory

Recent research has demonstrated that loss of financial capacity is a common consequence of Alzheimer's disease (AD). While progressive cognitive decline is a defining feature of AD, the relationship between such decline and loss of financial capacity in AD remains unclear. Working memory may be strongly associated with financial abilities, as many financial tasks require temporary storage and manipulation of numerical and other data. The present study examined the relationship between financial capacity and working memory in AD patients. Participants included 20 AD patients and 23 cognitively intact older controls. Working memory was conceptualized using Baddeley and colleagues' model, which posits that the three components of the working memory system are the visuospatial sketchpad, phonological loop, and central executive system. The present study examined only the latter two components of working memory. Each participant was administered the Financial Capacity Instrument (FCI), an instrument that directly assesses eight domains of financial activity, and the WAIS-III Working Memory subtests (Digit Span, Arithmetic, Letter–Number Sequencing). AD patients as a group performed significantly below controls on the FCI Total Score and on each of the eight FCI domains and working memory subtests. Within the AD group, measures of the central executive component of working memory (WAIS-III Digits Backward, Arithmetic, and Letter-Number Sequencing tests) showed strong correlations with the FCI domains of basic monetary skills, checkbook management, bank statement management, and bill payment and FCI total score, while a measure of the phonological loop component of working memory (WAIS-III Digits Forward) was not significantly correlated with any FCI domains or with the FCI total score. The results suggest that the multiple domains of financial capacity are primarily correlated with the central executive component of working memory.     

A microcomputer program for evaluating WISC-R factor scores

A data analysis routine was developed for the Apple II series microcomputer that allows school psychologists to quickly calculate WISC-R factor scores and evaluate the significance of differences between the factors and individual subtest deviations within the Verbal Comprehension and Perceptual Organization factors. The source code written in Applesoft BASIC is provided. With minor modifications the program can be adapted to run on other computer systems.     

Two-subtest estimations of WAIS-III factor index scores

The reliability and validity of various short forms of the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III; D. Wechsler, 1997) were evaluated in a sample of 100 patients with traumatic brain injury and in a demographically matched subgroup from the standardization sample. All short forms were based on 2-subtest estimations of the respective factor indexes. Although acceptable estimates could be obtained from all short forms for Verbal Comprehension, none of the possible short forms for Perceptual Organization consistently met the minimum criterion regarding the percentage of cases that fell within the 90% confidence interval of the full-length index. It is concluded that short-form estimates of the WAIS-III are not appropriate for clinical use when the goal is to obtain factor indexes.     

Structure of the Mini-Mental State Examination: a comparison between normal and clinical subjects

The Mini-Mental State Examination was administered to a sample of 133 Italians ranging from 60 to 80 years of age. From a Principal Components Analysis three factors were retained, being results of both varimax and oblimin rotations. These were labeled (1) Memory, (2) Verbal Comprehension, and (3) Attention. These factors are similar to those obtained with normal elderly Americans, but they are different from the factors based on clinical samples. No age differences in the factor scores were found among the normal elderly subjects when education was considered. In contrast, significant differences were found between a group of 25 demented patients and a matched group randomly extracted from the normal sample.     

Four tables for the statistical interpretation of factor scores on the Wechsler intelligence scale for children—Revised (WISC-R)

When the Wechsler Intelligence Scale for Children–Revised (WISC-R) is analyzed into three factors (Verbal Comprehension, Perceptual Organization, and Freedom From Distractibility), the clinician has the choice of expressing each factor as either a deviation quotient (an IQ analog) or a factor score (the arithmetic mean of the constituent subtests). For the clinician who wishes to use factor scores instead of deviation quotients, four tables are presented that provide (1) the percentile equivalents of factor scores; (2) the significance of differences between factor scores; (3) the frequency with which specified discrepancies occur; and (4) the significance of differences between a factor score and the scaled score of a constituent subtest.     

Age-related invariance of abilities measured with the Wechsler Adult Intelligence Scale--III

Examination of measurement invariance tests the assumption that the model underlying a set of test scores is directly comparable across groups. The observation of measurement invariance provides fundamental evidence for the inference that scores on a test afford equivalent measurement of the same psychological traits among diverse groups. Groups may be derived from different psychosocial backgrounds or different clinical presentations. In the Wechsler Adult Intelligence Scale-III (WAIS-III)/Wechsler Memory Scale-III (WMS-III) Technical Manual (Psychological Corporation, 2002), there appears to be a breakdown in factor structure among the standardization cases in older adults. In this study, the authors evaluated the invariance of the measurement model of the WAIS-III across 5 age bands. All components of the measurement model were examined. Overall, the evidence pointed to invariance across age of a modified 4-factor model that included cross-loadings for the Similarities and Arithmetic subtests. These results support the utility of the WAIS-III as a measure of stable intelligence traits across a wide age range.     

Executive function and psychosocial adjustment in healthy children and adolescents: A latent variable modelling investigation

The objective of this study was to establish latent executive function (EF) and psychosocial adjustment factor structure, to examine associations between EF and psychosocial adjustment, and to explore potential development differences in EF-psychosocial adjustment associations in healthy children and adolescents. Using data from the multisite National Institutes of Health (NIH) magnetic resonance imaging (MRI) Study of Normal Brain Development, the current investigation examined latent associations between theoretically and empirically derived EF factors and emotional and behavioral adjustment measures in a large, nationally representative sample of children and adolescents (7–18 years old; N = 352). Confirmatory factor analysis (CFA) was the primary method of data analysis. CFA results revealed that, in the whole sample, the proposed five-factor model (Working Memory, Shifting, Verbal Fluency, Externalizing, and Internalizing) provided a close fit to the data, χ²(66) = 114.48, p < .001; RMSEA = .046; NNFI = .973; CFI = .980. Significant negative associations were demonstrated between Externalizing and both Working Memory and Verbal Fluency (p < .01) factors. A series of increasingly restrictive tests led to the rejection of the hypothesis of invariance, thereby precluding formal statistical examination of age-related differences in latent EF-psychosocial adjustment associations. Findings indicate that childhood EF skills are best conceptualized as a constellation of interconnected yet distinguishable cognitive self-regulatory skills. Individual differences in certain domains of EF track meaningfully and in expected directions with emotional and behavioral adjustment indices. Externalizing behaviors, in particular, are associated with latent Working Memory and Verbal Fluency factors.     

Orthogonal higher order structure and confirmatory factor analysis of the French Wechsler Adult Intelligence Scale (WAIS-III)

According to the most widely accepted Cattell-Horn-Carroll (CHC) model of intelligence measurement, each subtest score of the Wechsler Intelligence Scale for Adults (3rd ed.; WAIS-III) should reflect both 1st- and 2nd-order factors (i.e., 4 or 5 broad abilities and 1 general factor). To disentangle the contribution of each factor, we applied a Schmid-Leiman orthogonalization transformation (SLT) to the standardization data published in the French technical manual for the WAIS-III. Results showed that the general factor accounted for 63% of the common variance and that the specific contributions of the 1st-order factors were weak (4.7%-15.9%). We also addressed this issue by using confirmatory factor analysis. Results indicated that the bifactor model (with 1st-order group and general factors) better fit the data than did the traditional higher order structure. Models based on the CHC framework were also tested. Results indicated that a higher order CHC model showed a better fit than did the classical 4-factor model; however, the WAIS bifactor structure was the most adequate. We recommend that users do not discount the Full Scale IQ when interpreting the index scores of the WAIS-III because the general factor accounts for the bulk of the common variance in the French WAIS-III. The 4 index scores cannot be considered to reflect only broad ability because they include a strong contribution of the general factor.     

WISC-R subtest but no overall VIQ-PIQ difference in Dutch children with PDD-NOS

VIQ-PIQ differences have been studied in children with autism and Asperger syndrome but have not been studied in a separate group of children with PDD-NO, although, PDD-NOS has a much higher prevalence rate than autism and deficits in communication and social interaction are severe. The Wechsler Intelligence Scale for Children-Revised (WISC-R) was administered to 100 children, aged 6-12 years, with PDD-NOS (n = 76), autism (n = 13), and Asperger syndrome (n = 11). PDD-NOS was diagnosed using explicit research criteria. No overall differences between VIQ and PIQ were found in PDD-NOS and autism. Peaks in the subtest scores on Information, Similarities, Picture Arrangement, and Mazes, and troughs in the subtest scores on Comprehension, Digit Span, and Coding were demonstrated in children with PDD-NOS. Their score on the Freedom from Distractibility factor was lower than the scores on the Verbal Comprehension factor and the Perceptual Organization factor. Children with PDD-NOS seemed to have a similar VIQ-PIQ profile as children with autism, and on the subtest level children with PDD-NOS showed some similarities to children with Asperger syndrome or autism. It was not possible to distinguish PDD-NOS from autism or Asperger syndrome by using IQ scores.     

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.     

WISC-R Subtest But No Overall VIQ–PIQ Difference in Dutch Children with PDD-NOS

VIQ–PIQ differences have been studied in children with autism and Asperger syndrome but have not been studied in a separate group of children with PDD-NO, although, PDD-NOS has a much higher prevalence rate than autism and deficits in communication and social interaction are severe. The Wechsler Intelligence Scale for Children-Revised (WISC-R) was administered to 100 children, aged 6–12 years, with PDD-NOS (n = 76), autism (n = 13), and Asperger syndrome (n = 11). PDD-NOS was diagnosed using explicit research criteria. No overall differences between VIQ and PIQ were found in PDD-NOS and autism. Peaks in the subtest scores on Information, Similarities, Picture Arrangement, and Mazes, and troughs in the subtest scores on Comprehension, Digit Span, and Coding were demonstrated in children with PDD-NOS. Their score on the Freedom from Distractibility factor was lower than the scores on the Verbal Comprehension factor and the Perceptual Organization factor. Children with PDD-NOS seemed to have a similar VIQ–PIQ profile as children with autism, and on the subtest level children with PDD-NOS showed some similarities to children with Asperger syndrome or autism. It was not possible to distinguish PDD-NOS from autism or Asperger syndrome by using IQ scores.     

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.     

A confirmatory factor analysis of the California Verbal Learning Test--Second Edition (CVLT-II) in the standardization sample

The purpose of this study is to determine the latent structure of the California Verbal Learning Test-Second Edition (CVLT-II; Delis, Kramer, Kaplan, & Ober, 2000) at three different age levels, using the standardization sample. Maximum likelihood confirmatory factor analyses are performed to test four competing hypothetical models for fit and parsimony. A four-factor model consisting of Attention Span, Learning Efficiency, Delayed Memory, and Inaccurate Memory provides the best fit to the data at two age levels (16-30 years and 31-60 years, respectively) but the factor structure is somewhat less robust in the oldest age group (>60 years). The results clarify the latent structure of the CVLT-II and suggest that a multifactorial interpretation of quantitative and qualitative indexes from this instrument is appropriate for clinical practice with most adults, although findings may need to be interpreted more cautiously among older persons.