Analysis of WAIS-IV index score scatter using significant deviation from the mean index score

The Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) does not include verbal IQ and performance IQ scores, as provided in previous editions of the scale; rather, this edition provides comparisons among four index scores, allowing analysis of an individual's WAIS-IV performance in more discrete domains of cognitive ability. To supplement the pairwise index score comparisons included in the WAIS-IV manuals, this article describes the use of the mean of the four index scores (the average index score) as a baseline for analyzing index score variability and as a method for identifying strengths and weaknesses within an individual's index score pattern. Davis's formula was used to calculate critical values for the identification of index scores with a statistically significant difference from the average index score. Subsequent analysis of the WAIS-IV normative sample indicates that variability in performance at the index score level is not uncommon in the general population. More than 70% of individuals in the normative sample have at least one index score that differs significantly from their mean index score. This variability in index score performance appears to have little relationship to age or gender, but it is strongly related to the full-scale IQ.     

Some supplementary methods for the analysis of the Delis-Kaplan Executive Function System

Supplementary methods for the analysis of the Delis-Kaplan Executive Function System (Delis, Kaplan, & Kramer, 2001) are made available, including (a) quantifying the number of abnormally low achievement scores exhibited by an individual and accompanying this with an estimate of the percentage of the normative population expected to exhibit at least this number of low scores; (b) estimating the overall abnormality of an individual's achievement score profile with the Mahalanobis distance index; (c) calculating a composite executive function index score for an individual and providing accompanying confidence limits; and (d) providing the percentile ranks for an individual's achievement scores and executive index score (in the latter case, confidence limits on scores are also expressed as percentile ranks). With the exception of the Mahalanobis distance index, all the methods can be obtained with the equations and tables provided in this article. However, for the convenience of clinicians and to reduce the possibility of clerical error, the methods have also been implemented in a computer program. More important, the program allows the methods to be applied when only a subset of scores is available. The program can be downloaded (as a zip file) from this article's supplemental materials or from www.abdn.ac.uk/~psy086/dept/DKEFS_Supplementary_Analysis.htm.     

Some supplementary methods for the analysis of the RBANS

Supplementary methods for the analysis of the Repeatable Battery for the Assessment of Neuropsychological Status are made available, including (a) quantifying the number of abnormally low Index scores and abnormally large differences exhibited by a case and accompanying this with estimates of the percentages of the normative population expected to exhibit at least this number of low scores and large differences, (b) estimating the overall abnormality of a case's Index score profile using the Mahalanobis Distance Index (MDI), (c) reporting confidence limits on differences between a case's Index scores, and (d) offering the option of applying a sequential Bonferroni correction when testing for reliable differences. With the exception of the MDI, all the methods can be obtained using the formulas and tables provided in this article. However, for the convenience of clinicians, and to reduce the possibility of clerical error, the methods have also been implemented in a computer program. More importantly, the program allows the methods to be applied when only a subset of the Indexes is available. The program can be downloaded from www.abdn.ac.uk/~psy086/dept/RBANS_Supplementary_Analysis.htm     

Bifactor Modeling and the Estimation of Model-Based Reliability in the WAIS-IV

Previous confirmatory factor analytic research that has examined the factor structure of the Wechsler Adult Intelligence Scale–Fourth Edition (WAIS-IV) has endorsed either higher order models or oblique factor models that tend to amalgamate both general factor and index factor sources of systematic variance. An alternative model that has not yet been examined for the WAIS-IV is the bifactor model. Bifactor models allow all subtests to load onto both the general factor and their respective index factor directly. Bifactor models are also particularly amenable to the estimation of model-based reliabilities for both global composite scores (ω _h ) and subscale/index scores (ω _s ). Based on the WAIS-IV normative sample correlation matrices, a bifactor model that did not include any index factor cross loadings or correlated residuals was found to be better fitting than the conventional higher order and oblique factor models. Although the ω _h estimate associated with the full scale intelligence quotient (FSIQ) scores was respectably high (.86), the ω _s estimates associated with the WAIS-IV index scores were very low (.13 to .47). The results are interpreted in the context of the benefits of a bifactor modeling approach. Additionally, in light of the very low levels of unique internal consistency reliabilities associated with the index scores, it is contended that clinical index score interpretations are probably not justifiable.     

Scores composites CHC pour la WAIS-IV : normes francophones

Results from contemporary research have demonstrated the importance of fluid reasoning, working memory and processing speed in cognitive functioning. The developers of the WAIS-IV have introduced new subtests to strengthen the assessment of these cognitive dimensions. The interpretation of the WAIS-IV is currently based on four factorial indexes (VCI, PRI, WMI, and PSI), as well as on the FSIQ. The developers of the WAIS-IV indicated that one of the objectives of the revision was to update the theoretical foundations of this intelligence scale. However, the overall structure of the WAIS-IV is not aligned with the consensual Cattell-Horn-Carroll (CHC) theory of cognitive abilities. For instance, the technical manual of the WAIS-IV does not provide an index of fluid reasoning, although the authors emphasized the importance of this dimension in cognitive functioning. In this paper, we provide the French normative tables for five CHC composite scores of the WAIS-IV, namely, fluid reasoning (Gf), comprehension-knowledge (Gc), visual processing (Gv), short-term memory (Gsm), and processing speed (Gs). These norms were created using a statistical approximation procedure. Like the CHC norms that we have proposed for the WISC-IV, theses tables allow clinicians to switch towards the dominant interpretative framework and to use the CHC composite scores as complementary measures to the four standard index scores, in order to conduct normative and ipsative analyses.     

How Many is Enough? Determining Optimal Sample Sizes for Normative Studies in Pediatric Neuropsychology

The purpose of this investigation was to determine how confidence intervals (CIs) for pediatric neuropsychological norms vary as a function of sample size, and to determine optimal sample sizes for normative studies. First, the authors calculated 95% CIs for a set of published pediatric norms for four commonly used neuropsychological instruments. Second, 95% CIs were calculated for varying sample size (from n?=?5 to n?=?500). Results suggest that some pediatric norms have unacceptably wide CIs, and normative studies ought optimally to use 50 to 75 participants per cell. Smaller sample sizes may lead to overpathologizing results, while the cost of obtaining larger samples may not be justifiable.     

How many is enough? Determining optimal sample sizes for normative studies in pediatric neuropsychology.

The purpose of this investigation was to determine how confidence intervals (CIs) for pediatric neuropsychological norms vary as a function of sample size, and to determine optimal sample sizes for normative studies. First, the authors calculated 95% CIs for a set of published pediatric norms for four commonly used neuropsychological instruments. Second, 95% CIs were calculated for varying sample size (from n = 5 to n = 500). Results suggest that some pediatric norms have unacceptably wide CIs, and normative studies ought optimally to use 50 to 75 participants per cell. Smaller sample sizes may lead to overpathologizing results, while the cost of obtaining larger samples may not be justifiable.     

The Prospective and Retrospective Memory Questionnaire (PRMQ): Normative data and latent structure in a large non-clinical sample

The Prospective and Retrospective Memory Questionnaire (PRMQ; Smith, Della Sala, Logie, & Maylor, 2000) was developed to provide a self-report measure of prospective and retrospective memory slips in everyday life. It consists of sixteen items, eight asking about prospective memory failures, and eight concerning retrospective failures. The PRMQ was administered to a sample of the general adult population (N = 551) ranging in age between 17 and 94. Ten competing models of the latent structure of the PRMQ were derived from theoretical and empirical sources and were tested using confirmatory factor analysis. The model with the best fit had a tripartite structure and consisted of a general memory factor (all items loaded on this factor) plus orthogonal specific factors of prospective and retrospective memory. The reliabilities (internal consistency) of the Total scale and the Prospective and Retrospective scales were acceptable: Cronbach's alpha was 0.89, 0.84, and 0.80, respectively. Age and gender did not influence PRMQ scores, thereby simplifying the presentation and interpretation of normative data. To ease interpretation of scores on the PRMQ, tables are presented for conversion of raw scores on the Total scale and Prospective and Retrospective scales to T scores (confidence limits on scores are also provided). In addition, tables are provided to allow users to assess the reliability and abnormality of differences between an individual's scores on the Prospective and Retrospective scales.     

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.     

Discrepancies between standardized measures of cognitive level and Halstead-Reitan impairment indices as inferences of brain damage following head injuries

z scores for measures of intelligence, memory, educational achievement, and neuropsychological impairment were obtained for 193 patients who had sustained impacts of mechanical energy to their skulls. Two sets of normative data, adjusted for age and sex and not adjusted for these variables, were employed to compute indices of neurocognitive proficiency (the inverse of impairment). 80% or 76 of the 96 patients whose Halstead-Reitan Indices were greater than 0.4 displayed scores for neurocognitive proficiency that were two or more standard deviations below the averages of their scores for intelligence, memory, and educational achievement. None of the patents whose Impairment Indices were 0.4 or less displayed this discrepancy. There were no statistically significant differences between these two groups of patients with respect to the presence of unconsciousness following the injury or the duration of posttraumatic memory disruptions. The results indicate that quantitative scores for neuropsychological impairments are still the most accurate criteria to discern brain dysfunction within the mild to moderate range.     

Cerebral perfusion and neuropsychological follow up in mild traumatic brain injury: Acute versus chronic disturbances?

In a subgroup of patients with mild traumatic brain injury (TBI) residual symptoms, interfering with outcome and return to work, are found. With neuropsychological assessment cognitive deficits can be demonstrated although the pathological underpinnings of these cognitive deficits are not fully understood. As the admission computed tomography (CT) often is normal, perfusion CT imaging may be a useful indicator of brain dysfunction in the acute phase after injury in these patients.In the present study, directly after admission perfusion CT imaging was performed in mild TBI patients with follow-up neuropsychological assessment in those with complaints and a normal non-contrast CT. Neuropsychological tests comprised the 15 Words test Immediate Recall, Trailmaking test part B, Zoo Map test and the FEEST, which were dichotomized into normal and abnormal. Perfusion CT results of patients with normal neuropsychological test scores were compared to those with abnormal test scores.In total eighteen patients were included. Those with an abnormal score on the Zoo Map test had a significant lower CBV in the right frontal and the bilateral parieto-temporal white matter. Patients with an abnormal score on the FEEST had a significant higher MTT in the bilateral frontal white matter and a significant decreased CBF in the left parieto-temporal grey matter. No significant relation between the perfusion CT parameters and the 15 Words test and the Trailmaking test part B was present.In conclusion, impairments in executive functioning and emotion perception assessed with neuropsychological tests during follow up were related to differences in cerebral perfusion at admission in mild TBI. The pathophysiological concept of these findings is discussed.     

Statistical significance and reliability of single-subtest and cluster deviation scores

Suppose one has a battery of K subtests and a composite for the battery is defined as the mean of the K standardized subtest scores. An individual's single-subtest deviation score is the difference between the individual's score on any single subtest and his composite score. A cluster deviation score is the difference between an examinee's average for a small set (cluster) of subtests and his composite. Formulas are given for the test of statistical significance of the individual's subtest or cluster deviation score and the internal consistency reliability of such deviation scores.     

On the "optimal" size for normative samples in neuropsychology: capturing the uncertainty when normative data are used to quantify the standing of a neuropsychological test score.

Bridges and Holler (2007) have provided a useful reminder that normative data are fallible. Unfortunately, however, their paper misleads neuropsychologists as to the nature and extent of the problem. We show that the uncertainty attached to the estimated z score and percentile rank of a given raw score is much larger than they report and that it varies as a function of the extremity of the raw score. Methods for quantifying the uncertainty associated with normative data are described and used to illustrate the issues involved. A computer program is provided that, on entry of a normative sample mean, standard deviation, and sample size, provides point and interval estimates of percentiles and z scores for raw scores referred to these normative data. The methods and program provide neuropsychologists with a means of evaluating the adequacy of existing norms and will be useful for those planning normative studies.     

A brief (one-hour) quantitative neuropsychological assessment with three performance-based tests: strong concordance with proficiency scores for a more extensive test battery

Raw scores for each of several dozens of traditional and more recently developed neuropsychological tests were correlated with an impairment index composed of all of these scores from the records of 162 patients who had been assessed following impacts of substantial mechanical energies. A score of either less than 20 correct binaural responses for a dichotic word listening task, more than 99 sec. for Trails B, and more than 3.8 min. to complete the Tactual Performance Test with both hands correctly classified 85% of patients whose z scores were less than -1.0 (below average) or -1.0 or above (average) for a composite neurocognitive index. The results suggest that these three tests, administrable within about one hour, may be employed as a more objective criterion rather than "clinical impressions" for discerning if patients require more extensive neuropsychological testing.     

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.     

A data-driven approach to neuropsychological features in isolated REM behaviour disorder: A latent class analysis

Recent evidence demonstrated that neuropsychological assessment may be considered a valid marker of neurodegeneration in idiopathic REM sleep behaviour disorder (iRBD). However, little is known about the possible neuropsychological heterogeneity within the iRBD population. This retrospective study aimed to identify and describe different neuropsychological phenotypes in iRBD patients by means of a data-driven approach using latent class analysis. A total of 289 iRBD patients underwent a neuropsychological assessment evaluating cognitive domains: global cognition, language, short- and long-term memory, executive functions and visuospatial abilities. The presence of mild cognitive impairment (MCI) was also assessed. Latent class analysis was carried out to identify iRBD subtypes according to neuropsychological scores. The most parsimonious model identified three latent classes. Groups were labelled as follows: Class 2 “severely impaired” (n = 83/289): mean pathological scores in different tests, a high percentage of MCI multiple-domain and impairment in all neuropsychological domains. Class 1 “moderately impaired” (n = 44/289): mean neuropsychological score within the normal value, a high percentage of MCI (high risk to phenoconversion) and great impairment in the visuospatial domain. Class 3 “slightly impaired” (n = 162/289): no deficit worthy of attention except for short- and long-term memory. Our results suggest three different clinical phenotypes within the iRBD population. These findings may be relevant in the future for predicting the clinical trajectories of phenoconversion in iRBD.     

Neuropsychological functioning in kleptomania

Kleptomania is characterized by the failure to resist impulses to steal objects not needed for personal use or their monetary value. The objective of this study was to examine cognitive and executive functioning in subjects with kleptomania. Fifteen women with a primary DSM-IV diagnosis of kleptomania underwent a detailed psychiatric examination, including measures of kleptomania severity, and a battery of neuropsychological tests that emphasized executive functions. Correlational analyses were computed between measures of kleptomania severity and tests of executive functioning. Kleptomania subjects reported a mean duration of illness of 17.9 years and shoplifting a mean of 1.7 times per week. All subjects reported an inability to resist urges to shoplift. Neuropsychological testing revealed group mean test scores within 0.5 standard deviations of normative standards for age. Five subjects (33.3%), however, had below-average performance on at least one measure of executive functioning, and 4 (26.7%) had below-average scores on two executive measures. Correlational analyses revealed a statistically significant correlation between kleptomania severity and Wisconsin Card Sorting Test performance (r=-0.693, p=0.004). As a group, subjects with kleptomania did not demonstrate deficits on neuropsychological testing. Greater kleptomania symptom severity, however, was correlated with impairment in executive functioning.     

Influence of IQ in interpreting MMSE scores in patients with multiple sclerosis

The Mini-Mental State Examination (MMSE) and Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) were administered to 46 outpatients diagnosed with multiple sclerosis (MS). MMSE total raw score was significantly and positively correlated with all WAIS-IV indexes, even when controlling for the effects of participant educational level, with the strongest relationship being with Full Scale IQ. These results suggest that clinicians consider patient intellectual functioning, in particular Full Scale IQ, when diagnosing neurocognitive impairment based on screening with the MMSE in individuals with MS.     

The woodcock reading mastery test: impact of normative changes

This study examined the magnitude of differences in standard scores, convergent validity, and concurrent validity when an individual's performance was gauged using the revised and the normative update (Woodcock, 1998) editions of the Woodcock Reading Mastery Test in which the actual test items remained identical but norms have been updated. From three metropolitan areas, 899 first to third grade students referred by their teachers for a reading intervention program participated. Results showed the inverse Flynn effect, indicating systematic inflation averaging 5 to 9 standard score points, regardless of gender, IQ, city site, or ethnicity, when calculated using the updated norms. Inflation was greater at lower raw score levels. Implications for using the updated norms for identifying children with reading disabilities and changing norms during an ongoing study are discussed.     

WAIS-III percentile scores by education and sex for U.S. and Canadian populations

Tables are presented for the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III) IQ and index scores by education level for both the U.S. and Canadian normative samples. This allows clinicians to provide more accurate identification of relative strengths or weaknesses, compared to expectations from an individual's background, rather than the general population. Because sex differences are notable on the Processing Speed Index, data for this measure are presented separately. The similarities and differences between the two national samples are noted, with particular reference to the relatively weaker demographic effects found in the Canadian sample.