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.     

Adult age and digit symbol substitution performance: a meta-analysis

This article reports the results of a meta-analysis of the effects of age, education, and estimated year of measurement on scores from the Wechsler Adult Intelligence Scale and the Wechsler Adult Intelligence Scale-Revised Digit Symbol Substitution Test. Analysis of effect sizes for age reported in 141 studies published between 1986 and 2002 indicated a mean standardized difference of -2.07. Age accounted for 86% of the variance in a regression model using age, education, and year submitted as predictors of Digit Symbol scores. There was no association between years of education or year submitted and Digit Symbol scores for younger adults or older adults.     

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.     

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.     

Wechsler Adult Intelligence Scale-Third Edition short form for index and IQ scores in a psychiatric population

An eight-subtest short form (SF8) of the Wechsler Adult Intelligence Scale, Third Edition (WAIS-III), maintaining equal representation of each index factor, was developed for use with psychiatric populations. Data were collected from a mixed inpatient/outpatient sample (99 men and 101 women) referred for neuropsychological assessment. Psychometric analyses revealed an optimal SF8 comprising Vocabulary, Similarities, Arithmetic, Digit Span, Picture Completion, Matrix Reasoning, Digit Symbol Coding, and Symbol Search, scored by linear scaling. Expanding on previous short forms, the current SF8 maximizes the breadth of information and reduces administration time while maintaining the original WAIS-III factor structure.     

Decoding digit symbol: speed,memory, and visual scanning

The authors evaluated the relative contributions of speed, memory, and visual scanning to Digit Symbol score in a sample of young adults (N = 87). Speed (Symbol Copy) explained 35% of Digit Symbol variance; only half of this was attributable to graphomotor speed (Name Printing), implying a role for perceptual speed. Visual-scanning tests (e.g., Symbol Scan) explained (on average) 34% of Digit Symbol variance, much of which was independent of perceptual-motor speed, establishing an important role for visual-scanning efficiency in Digit Symbol performance. By contrast, memory tests (on average) explained only 4% to 5% of Digit Symbol variance: statistically significant but clearly subsidiary, although a visual memory composite correlated more strongly with Digit Symbol. The Digit Symbol incidental learning procedures did, however, correlate moderately with other memory measures, suggesting that they are valid memory screening devices.     

The Relationship Between Performance on the Gordon Diagnostic System and Other Measures of Attention

Tests purporting to measure attention were administered to college students to examine their relationship to three relatively new tests of attention from the Gordon Diagnostic System (GDS). All subjects received the Standard Delay, Vigilance, and Distractibility Tests of the GDS. In addition, 69 of 136 subjects received the Digit Span, Arithmetic, and Digit Symbol subtests of the Wechsler Adult Intelligence Scale-Revised (WAIS-R), and Kagan's Matching Familiar Figures Test. After the GDS, the other 67 subjects received the Visual Span subtest of the Wechsler Memory Scale-Revised (WMS-R), and the Stroop. Replication (across two studies) and gender influences were not evident on GDS performance. Performance data on this test for these 136 college students, collapsed across replication and gender, are presented. Although within-test correlations were strong, correlations between tests were weak. A ceiling effect on the Vigilance task may have effected its correlations with other tests. Results suggest that the GDS tasks are not substitutes for commonly used tests of attention, but may be useful as an additional source of information in the assessment of attention.     

Correlates of memory decline: a 4-year longitudinal study of older adults with memory complaints.

Change in memory performance and its correspondence to change in speed of performance and self-reported memory functioning were investigated longitudinally in 30 older adults with memory complaints. Subjects were assessed by self-report questionnaires and cognitive tests 3 times, at near 2-year intervals. A significant decline in word-recall scores was found, which was accompanied at the group level by significant self-reported decline in everyday memory functioning and nonsignificant decline in Wechsler Adult Intelligence Scale Digit Symbol scores (alpha = .05). The oldest subjects showed the most substantial declines in memory performance. At the individual level, however, memory change did not significantly correlate with either change in self-reports or change in Digit Symbol scores. Although these results do not support a cognitive slowing model of decline at the intraindividual level, they do have implications for intervention of age-related memory decline.     

Does high educational level protect against intellectual decline in older adults?: A 10‐year longitudinal study

This study examined the relation between educational level and intellectual change in Japanese older adults. Participants (age = 65–79 years, n = 593) comprised the first‐wave participants of the National Institute for Longevity Sciences‐Longitudinal Study of Aging (NILS‐LSA). They were followed for 10 years and were tested six times. Educational levels were divided into two groups (low‐educated or high‐educated), and intellectual changes for the 10 years were assessed using the Japanese Wechsler Adult Intelligence Scale‐Revised Short Forms (JWAIS‐R‐SF); subtests included Information, Similarities, Picture Completion, and Digit Symbol. General linear mixed‐model analyses revealed that education had not affected 10‐year changes of the Information, Similarities, and Picture Completion subtest scores. In contrast, education was significantly associated with a change in the Digit Symbol subtest score; individuals with higher levels of education showed greater decline than those with less education, although they had higher ability at every time point. These findings suggest that higher education does not protect against intellectual decline in late life, although it is associated with long‐term individual differences in intelligence.     

Interactions among affect, cognition, and visuomotor coordination as measured in words and symbols

The associative frequencies of responses to stimulus words during free and controlled forced-choice word-association tests correlate well with each other and with assessments of the affective character (emotional content) of the stimulus words for the test subjects (Osgood Index) for three samples of volunteer French undergraduate students (ns = 200, 64, and 72). These indices correlate negatively with the subjects' performance on Digit Symbol Substitution tests. Neisser's theory of schemata and Edelman's theory of neuronal group selection may provide insight into this relationship. If the associative frequency of a subject's response decreased, the affective content of the word stimulus (as perceived by the subject) diminished as well. This relationship was associated with a relatively higher score on Digit Symbol Substitution. Conversely, it was observed that subjects whose responses were characterized by high associative frequencies (whether the response was spontaneous or forced-choice) rated the stimulus words as having a relatively stronger affective content or emotional character and performed less well on Digit Symbol Substitution.     

Age, exercise, and coding performance

We investigated the effects of exercise on the coding performance of young and older subjects. Hypotheses were tested that exercise either facilitates spatial localization or reduces susceptibility to distraction in older subjects. In a balanced design, we administered Digit Symbol and Symbol Digit coding tasks to exercisers and nonexercisers at two age levels under conditions of low or high within-task interference. The findings showed higher performance by the exercisers than by the nonexercisers only at the older age level and only with the Symbol Digit task. These findings support the hypothesis that exercise compensates for a loss of spatial localization skills with age. We found no evidence that susceptibility to distraction either increased with age or was affected by chronic exercise.     

The Role of Long-Term Memory in Digit–Symbol Test Performance in Young and Older Adults

ABSTRACT

The psychological functions assessed by substitution tests, and the age-related performance decline, are not well understood. Here several aspects of long-term memory were manipulated across younger and older adults. A 45-page Digit–Symbol test was employed. Each page contained a 9-item digit symbol code-table and 9 response items. There were 9 study conditions with each condition deployed across 5 pages, or trials, of the test. The conditions were formed by crossing two within-subjects factors, each with 3 levels. The first factor, Digit Order, pertained to having the code table digits in numerical order vs. a pseudo-random order fixed across trials vs. a pseudo-random order that varied across trials. The second factor, Symbol Pairing, pertained to having a fixed digit–symbol pairing across trials vs. having a varying digit–symbol pairing across trials vs. having a novel set of 9 symbols introduced on each of the 5 trials. Including the additional factor, Age, resulted in a 2 × 3 × 3 mixed randomised block design. The older group was slowed, F(1, 22) = 17.267, p < .001, and overall-performance was poorer when the digits were arranged non-numerically, F(1,44) = 55.403, p < .001. An Age by Symbol–Order interaction indicated that use of novel symbols disadvantaged only the older participants, F(1, 44) = 6.577, p = .014. While there was no evidence that incidental paired-associate learning or spatial memory affect digit–symbol performance, symbol familiarity may be important to digit symbol test completion in older adults. The benefit of ordinally arranged digits in the coding table highlights a fundamental process difference between Digit–Symbol and Symbol–Digit test formats.     

The backward span of the Corsi Block-Tapping Task and its association with the WAIS-III Digit Span

The Corsi Block-Tapping Task measures visuospatial short-term and working memory, but a standardized backward condition is lacking. The authors present a standardized backward procedure that was examined in 246 healthy older adults (ages 50 to 92), comparing the results with the Digit Span subtest of the Wechsler Adult Intelligence Scale--Third Edition. Principal component analysis resulted in a two-factor model, dissociating a verbal and a spatial working-memory factor. Also the Corsi backward is not more difficult than the Corsi forward, in contrast to the Digit Span backward that is more difficult than the Digit Span forward. This may suggest that the Corsi Block-Tapping Task backward task relies on processing within working-memory's slave systems, whereas the Digit Span backward also relies on the central executive component of working memory. Finally, regression-based normative data and cutoff scores for older adults are presented for use in clinical practice.     

Working memory training improvements and gains in non-trained cognitive tasks in young and older adults

Previous studies on working memory training have indicated that transfer to non-trained tasks of other cognitive domains may be possible. The aim of this study is to compare working memory training and transfer effects between younger and older adults (n = 60). A novel approach to adaptive n-back training (12 sessions) was implemented by varying the working memory load and the presentation speed. All participants completed a neuropsychological battery of tests before and after the training. On average, younger training participants achieved difficulty level 12 after training, while older training participants only reached difficulty level 5. In younger participants, transfer to Verbal Fluency and Digit Symbol Substitution test was found. In older participants, we observed a transfer to Digit Span Forward, CERAD Delayed Recall, and Digit Symbol Substitution test. Results suggest that working memory training may be a beneficial intervention for maintaining and improving cognitive functioning in old age.     

Three-year stability of WISC-R factor scores for black and white, female and male children classified as learning-disabled

Wechsler Intelligence Scale for Children-Revised (WISC-R) test and retest scores for a homogeneous sample (N=322) of approximately equal numbers of black and white, female and male learning-disabled children were compared over 3 years for factor structure and factor structure stability. These analyses were also conducted with a subsample (N=229) of the total sample for whom Digit Span scores were available. The socioeconomic status of children in the sample was determined by parents' occupation. The results suggested that WISC-R factor structure was stable over 3 years. Two-and three-factor solutions were found for the total group; three factors were found when Digit Span was included in the analysis. Coefficients of congruence indicated factorial similarity between groups of black and white, female and male children classified as learning-disabled.     

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.     

Confirmatory factor analysis of the Wechsler Intelligence Scale for Children--Third Edition in an Australian clinical sample

A confirmatory factor analysis was conducted on the Wechsler Intelligence Scale for Children-Third Edition (WISC-III; D. Wechsler, 1991) with a sample of 579 Australian children referred for assessment because of academic difficulties in the classroom. The children were administered the WISC-III as part of the initial eligibility determination process for funding of special education services. The children were aged between 6 years and 16 years 7 months. One-, two-, three-, and four-factor models were tested. The four-factor model proposed in the WISC-III manual fit the data significantly better than all other models tested.     

Structure of the Wechsler Adult Intelligence Scale – Revised in the Italian Normal Standardisation Sample

Six multifactor correlated traits models and a single-factor model of the WAIS-R's factor pattern were examined by confirmatory maximum likelihood factor analyses of a data matrix from the WAIS-R's Italian normative sample raw scores (N=2284). The main aim was to identify what model(s) best fit(s) the data for the different age groups considered. Analyses were designed to determine which of seven hypothesised factor solutions best explained the intellectual ability of four age bands (16 to 74 years of age) and of all samples. Results showed the same three-correlated-factors model (Verbal, Performance, and Freedom From Distractibility) for the younger (16 to 24 years of age) and for more aged (65 to 74 years of age), and two different three-factor models for the adult (band from 25 to 64 years of age) that had in common the presence of Digit Symbol loading on Freedom From Distractibility, that in the younger and aged band loaded on Perceptual Organisation. The individuals may use different strategies when performing a given task on the WAIS-R. Such differences in latent variability may represent real differences in neuropsychological functioning, and as such can account for some of the variability in results noted in the literature. Differences in latent variability across distinct demographic and clinical groups could provide important insight into brain–behaviour relationships.     

Comparability, reliability, and practice effects on alternate forms of the Digit Symbol Substitution and Symbol Digit Modalities tests

The present study examined the comparability of 4 alternate forms of the Digit Symbol Substitution test and the Symbol Digit Modalities (written) test, including the original versions. Male contact-sport athletes (N = 112) were assessed on 1 of the 4 forms of each test. Reasonable alternate form comparability was demonstrated through establishing normality of form distributions and conducting pairwise form comparisons of means, variability, and intraclass correlations. Nonetheless, alternate forms are likely an insufficient means of controlling practice in speeded measures at brief (1-2 weeks) retest intervals. Reliable change indices demonstrated that practice must be accounted for in individual retesting.     

An automated version of the digit symbol substitution test (DSST)

An automated version of the Digit Symbol Substitution Test is described that employs a relatively inexpensive, commercially available microcomputer to present and score the task. Advantages of the automated DSST include: (1) objective scoring of both speed and accuracy of test performance, (2) printed copies of test scores, (3) convenient administration under standardized test conditions, and (4) the capacity for repeated assessment of an individual’s performance over time. Task performance data for individual subjects following doses of pentobarbital are presented; these data illustrate both the stability of task performance under constant conditions and the within-subjects sensitivity of task performance to experimental manipulations.