WAIS-R factor structure in Alzheimer's disease patients: a comparison of alternative models and an assessment of their generalizability

The WAIS-R is often used in neuropsychological evaluations of individuals with probable Alzheimer's disease (AD), but its factor structure in this population is unknown. Moreover, theories and past research findings make competing predictions concerning its structure. Using confirmatory factor analysis, the authors compared 5 alternative WAIS-R factor models among 516 AD patients: 1-factor (Spearman's g) and 2-factor (Verbal IQ and Performance IQ) models; a 3-factor model including Verbal Comprehension (VC), Perceptual Organization (PO), and Freedom From Distractibility (FD) factors; a 3-factor model in which Digit Symbol loads on PO rather than FD; and a 3-factor model in which Digit Symbol loads on both PO and FD. Results favored the 3-factor model in which Digit Symbol loads on PO rather than FD. Moreover, this model fit the data best among subsamples of patients defined by age, dementia severity, years of education, and gender.     

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.     

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).     

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.     

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.     

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.     

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.     

An examination for construct bias in the WISC-R across socioeconomic status

The ten subtests comprising the Wechsler Intelligence Scale for Children —Revised (WISC-R) were independently factor analyzed for middle and low socioeconomic status children. Two factors described the structure of the test in both cases. These two factors corresponded quite closely to the Verbal Comprehension and Perceptual Organization factors usually reported for the WISC-R. After testing for the equivalence of covariance matrices between the two socioeconomic status groups, coefficients of congruence between the factors were calculated. These coefficients indicated equivalence in the constructs being measured across the two groups.     

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 analysis of the WISC-R and the Adaptive Behavior Scale-School Edition for a referral sample

The purpose of this study was to determine if a common factor structure was evident in the Wechsler Intelligence Scale for Children-Revised (WISC-R) and the Adaptive Behavior Scale-School Edition (ABS-SE) for a sample of 171 children referred for evaluation of learning and behavior problems. The WISC-R subtests (excluding Mazes) and the ABS-SE factor domain scores (Personal Self-Sufficiency, Community Self-Sufficiency, Personal-Social Responsibility, Social Adjustment, and Personal Adjustment) were subjected to an exploratory principal-components factor analysis with varimax rotation. ANOVAs were conducted on each of the derived factors to determine race and sex effects. The results indicated no common factor structure in the instruments, the Verbal Comprehension, Perceptual Organization, Independent Functioning, Maladaptive Behavior, and Freedom From Distractibility factors being extracted. The derived factors were very similar to those identified in standardization data and other studies. Perceptual Organization and Social Adjustment showed sex and race effects, respectively, although each model accounted for only about 7% of the variance.     

Longitudinal models of developmental dynamics between reading and cognition from childhood to adolescence

The authors applied linear dynamic models to longitudinal data to examine the dynamics of reading and cognition from 1st to 12th grade. They used longitudinal data (N=445) from the Connecticut Longitudinal Study (S. E. Shaywitz, B. A. Shaywitz, J. M. Fletcher, & M. D. Escobar, 1990) to map the dynamic interrelations of various scales of the Wechsler Intelligence Scales for Children--Revised (i.e., Full, Performance, and Verbal) and specific markers of the Woodcock-Johnson Psycho-Educational Battery--Revised reading cluster (i.e., Letter-Word ID, Decoding, and Comprehension). The results of these analyses indicate that (a) there is a positive dynamic relation between reading and cognition across the selected age range; (b) this dynamic relation is symbiotic, with positive influences in both directions; (c) the influence from cognition to reading is stronger when considering the Wechsler Intelligence Scales for Children Performance--Revised Performance scale and weaker with the Verbal scale; (d) when examining the different Reading subtests, the influences from cognition are more apparent for Letter-Word ID and Comprehension and are less perceptible for Decoding; and (e) the dynamics of reading and cognition appear to be of stronger magnitude during 1st to 3rd grade, less strong during 4th to 8th grade, and weaker from 9th to 12th grade.     

The joint WAIS-III and WMS-III factor structure: development and cross-validation of a six-factor model of cognitive functioning

During the standardization of the Wechsler Adult Intelligence Scale (3rd ed.; WAIS-III) and the Wechsler Memory Scale (3rd ed.; WMS-III) the participants in the normative study completed both scales. This "co-norming" methodology set the stage for full integration of the 2 tests and the development of an expanded structure of cognitive functioning. Until now, however, the WAIS-III and WMS-III had not been examined together in a factor analytic study. This article presents a series of confirmatory factor analyses to determine the joint WAIS-III and WMS-III factor structure. Using a structural equation modeling approach, a 6-factor model that included verbal, perceptual, processing speed, working memory, auditory memory, and visual memory constructs provided the best model fit to the data. Allowing select subtests to load simultaneously on 2 factors improved model fit and indicated that some subtests are multifaceted. The results were then replicated in a large cross-validation sample (N = 858).     

The relationship between WAIS-R abilities and speed of processing in a word identification task

Matched to the proportions found in the U.K. census data for a range of demographic variables (age, sex, and socioeconomic status) 123 participants were tested on the Wechsler Adult Intelligence Scale-Revised (WAIS-R) and a test of the minimum presentation time required to identify tachistoscopically presented words. The correlations between the sum of the scaled scores for Full, Verbal, and Performance subtests and the log of the identification measures were -0.40, -0.22, and -0.51, respectively. These results are in line with those observed between the WAIS-R measures and standard visual inspection time (IT). Confirmatory factor analysis indicated that a three-factor model of intelligence with Verbal, Performance, and Attention/Concentration factors, and with the identification threshold loaded on the Performance factor alone, represented a better fit to the data than either a single general factor model or a two-factor model with Verbal and Performance factors. These results are in line with findings in the IT literature (Deary, 1993) that speed of information processing is significantly related to performance IQ but not to verbal IQ.     

Revisiting the factor structure of the WAIS-R: insights through nested factor modeling

Past attempts to model via confirmatory factor analysis (CFA) the Wechsler Adult Intelligence Scale-Revised (WAIS-R) intersubtest covariation have used an oblique factor or a higher order modeling approach. The attempts have failed to yield adequate model fit, based on current CFA recommendations. Using the WAIS-R standardization data, it is demonstrated that the WAIS-R can be better conceptualized as measuring a first-order general factor and three orthogonal group-level factors. The results are discussed in relation to Verbal and Performance Intelligence scoring and failed attempts to find relationships between VIQ/PIQ difference scores and external criteria. Because Arithmetic and Digit Span did not share any variance with the other VIQ subtests, independent of General Intelligence, clinicians should reconsider interpreting a VIQ score that includes information from Arithmetic and Digit Span in nonclinical populations. Researchers are encouraged to model intelligence factors as nested factor models, considering their superior model fit, and the increased clarity in the interpretations of relationships between IQ indices and criteria.     

Change and stability in adult intellectual functioning assessed by Wechsler item responses

Change in adult intellectual performance was assessed with longitudinal data from the Intergenerational Studies at the Institute of Human Development. Wechsler Intelligence data from two age cohorts spanning ages 18 to 61 were analyzed at the subtest and item level. Hotelling T2 analyses on sets of equivalent items from Wechsler subtests were studied to determine if change in response occurred between pairwise combinations of occasions of test administrations. We used Bowker's test to analyze data at the item level to determine the direction of change in performance. Consistent improvement in performance occurred between the ages of 18-40 and 18-54. Between the ages of 40 and 61, results showed mostly improved performance on the Information, Comprehension, and Vocabulary subtests, mixed change on the Picture Completion subtest, and decline on the Digit Symbol and Block Design subtests. The pattern of mixed change on the Picture Completion subtest indicated improvement on the easy items and decline on the difficult items. Decline in performance on the Block Design test occurred only for the most difficult items.     

Personality traits and critical thinking skills in college students: empirical tests of a two-factor theory

The two-factor theory defines critical thinking skills as a combined effect of cognitive abilities and personality dispositions. Although the available research supports the association between critical thinking and measures of cognitive ability, the specific traits contained in the dispositional factor have not been clearly identified through empirical research. In Study 1,101 undergraduate students completed the Watson-Glaser Critical Thinking Appraisal (WGCTA), three subtests of the Wechsler Adult Intelligence Scale-Third Edition, and the revised NEO Personality Inventory. Hierarchical multiple regression analyses showed that Openness to Experience scores accounted for significant incremental variance in WGCTA scores beyond that accounted for by Similarities subtest scores. In Study 2, similar analyses of data from 105 students also showed significant incremental effects for Openness to Experience, even after more variance in the cognitive factor was accounted for by the Verbal Comprehension Index. Implications of these findings for the enhancement of critical thinking skills in college students are discussed.     

Correlations for Wechsler Intelligence Scale for Children--Revised and the Wechsler Preschool and Primary Scale of Intelligence for Iranian children.

This study focused on the relationship between the Wechsler Intelligence Scale for Children--Revised (WISC--R) and the Wechsler Preschool and Primary Scale of Intelligence (WPPSI) given to 40 6-yr.-old Iranian children. Pearson correlations between the WISC--R and the WPPSI IQs and between scaled scores on the corresponding subtests were significant. The comparison of mean IQs and scaled scores indicates that the WISC--R yielded a significantly higher Verbal IQ and higher scores on Information, Vocabulary, Comprehension, and Picture Completion than the WPPSI. The mean difference between corresponding Verbal and Full Scale IQs was not significant. These results suggest that scores on the two instruments correlated well for these 6-yr.-old Iranian children and the content on which IQs for the recently restandardized WISC--R and WPPSI are based are related.     

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.     

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 Impact of Event Scale using a sample of World War II and Korean War veterans

This study assessed the factor structure of the Impact of Event Scale (IES), a measure of intrusion and avoidance, using a sample of World War II and Korean War veterans who had experienced combat 40-50 years earlier. A series of 3 confirmatory factor analytic models were specified and estimated using LISREL 8.3. Model 1 specified a 1-factor model. Model 2 specified a correlated 2-factor model. Model 3 specified a 2-factor model with additional cross-factor loadings for Items 2 and 12. Model 3 was found to fit the data. In addition, this model was found to be a better explanation of the data than the other models. Also in addition, the correlations between the Intrusion and Avoidance factors and the 4 subscales of the 28-item General Health Questionnaire were examined to determine the distinctiveness of the two IES factors.