Executive function, intellectual decline and daily living skills

Understanding the cognitive changes associated with compromised daily living skills in elderly individuals is important for making appropriate recommendations about the capacity for independent functioning. To this end, we retrospectively examined data from 92 elderly individuals presenting with cognitive decline who were administered measures of executive functioning, general intelligence, and daily living skills. Multiple regression analyses were used to examine the relationship between executive functioning and daily living skills, while controlling for age, depression, and either IQ decline or current IQ. Executive functioning accounted for additional variance in a broad range of daily living skills after controlling for IQ decline. When FSIQ was used in the regression model rather than IQ decline, executive functioning was no longer uniquely associated with daily living skills. Executive functions appear to be important for daily living skills until a critical threshold of low intellectual functioning is reached, reflecting the combined influence of premorbid ability and the extent of intellectual decline. Our results suggest that understanding the relative contribution of different cognitive domains to functional decline in elderly individuals should take into account general intellectual functioning and estimated decline, and that the initiation and/or persistence of self-directed cognitive processes may be important for adaptive daily functioning. These findings have implications for making more evidence-based recommendations about the capacity for independent living.     

Executive Function,Intellectual Decline and Daily Living Skills

ABSTRACT

Understanding the cognitive changes associated with compromised daily living skills in elderly individuals is important for making appropriate recommendations about the capacity for independent functioning. To this end, we retrospectively examined data from 92 elderly individuals presenting with cognitive decline who were administered measures of executive functioning, general intelligence, and daily living skills. Multiple regression analyses were used to examine the relationship between executive functioning and daily living skills, while controlling for age, depression, and either IQ decline or current IQ. Executive functioning accounted for additional variance in a broad range of daily living skills after controlling for IQ decline. When FSIQ was used in the regression model rather than IQ decline, executive functioning was no longer uniquely associated with daily living skills. Executive functions appear to be important for daily living skills until a critical threshold of low intellectual functioning is reached, reflecting the combined influence of premorbid ability and the extent of intellectual decline. Our results suggest that understanding the relative contribution of different cognitive domains to functional decline in elderly individuals should take into account general intellectual functioning and estimated decline, and that the initiation and/or persistence of self-directed cognitive processes may be important for adaptive daily functioning. These findings have implications for making more evidence-based recommendations about the capacity for independent living.     

Discrepancies between premorbid and current IQ as a function of progressive mental deterioration

The declining cognitive functioning typically found in patients with Alzheimer's disease presents an opportunity to study that decline. The changing magnitude of ever widening discrepancies between premorbid estimators of IQ and observed IQ increases as severity of the disease increases. Premorbid IQs estimated by these scores (the National Adult Reading Test-Revised, the reading tests of the Revised and Third Editions of the Wide Range Achievement Test, and a demographically based regression index for the Wechsler Adult Intelligence Scale-Revised) had relatively similar discrepancies from obtained WAIS-R Full Scale IQs in samples of normal elderly (n = 30), and elderly patients diagnosed with mild (n = 30) and moderate Alzheimer's disease (n = 30) dementia. The discrepancies became larger, regardless of premorbid estimator, as disease severity progressed from none to mild to moderate across the samples.     

Biased estimators, biased experts, and the Ivory Tower: a reply to Grove (2001)

This reply responds to W. M. Grove's (2001) critique of H. O. F. Veiel and R. F. Koopman's (2001) article on bias in widely used methods of estimating premorbid IQ. In this reply, the authors show that Grove is misrepresenting part of Veiel and Koopman's arguments, extend them to show that the proposed adjustment to regression estimates of IQ not only is unbiased but also is the maximum-likelihood estimate of the true IQ, and argue that Grove's notion of the acceptability of biased methods in judicial proceedings reflects a fundamental misapprehension of their nature and purpose.     

Recurrent severe hypoglycemia, intelligence, and speed of information processing

In a previous study, the cumulative effect of recurrent severe hypoglycemia on cognitive function was examined in 100 patients with insulin-treated diabetes and a significant correlation was observed between the frequency of severe hypoglycemic episodes and the difference between their current IQ and estimated premorbid IQ (Langan, Deary, Hepburn, & Frier, 1991). The study here extended this model for examination of the role of biological environmental influences on intelligence. Eighty-five of the original cohort of 100 patients were recalled and tested on Wechsler Performance IQ, a test of premorbid IQ, the Hick Reaction Time task, the Sternberg Memory Scan task and a test of Rapid Visual Information Processing (RVIP). The patients' frequency of severe hypoglycemia was assessed using a structured interview. Both IQ-decrement estimates and frequencies of severe hypoglycemia proved reliable after 18 months (correlations > .75) and the corrected correlation between these two variables was about .4. Therefore, repeated episodes of acute severe neuroglycopenia are associated with a lowering of IQ. Frequency of severe hypoglycemia was significantly related to Hick decision times and to response thresholds in the RVIP task. Factor analysis suggested that hypoglycemia affects decision or response-initiation processes rather than encoding, storage, comparison, or classification processes in short-term memory. Indices of these short-term memory processes were highly related to IQ-type test scores. This study also confirms, in a sample with a near-normal distribution of IQ, that measures of psychometric intelligence are significantly correlated with indices from elementary cognitive tests, especially RVIP task, which is based on signal-detection theory.     

On the relation between demographic variables and neuropsychological test performance

This paper reports a study of the relation between demographic variables and neuropsychological test performance in a sample of 141 normal subjects. A preliminary analysis demonstrated the importance of age, educational level, sex, and Verbal IQ for the prediction of neuropsychological test performance. The main study is a detailed analysis of the relation between these four variables and neuropsychological test performance. The results are presented in the form of standardized regression coefficients and are discussed in relation to the problem of predicting expected premorbid performance in neuropsychological tests.     

Scholastic Assessment or g? The relationship between the Scholastic Assessment Test and general cognitive ability

There is little evidence showing the relationship between the Scholastic Assessment Test (SAT) and g (general intelligence). This research established the relationship between SAT and g, as well as the appropriateness of the SAT as a measure of g, and examined the SAT as a premorbid measure of intelligence. In Study 1, we used the National Longitudinal Survey of Youth 1979. Measures of g were extracted from the Armed Services Vocational Aptitude Battery and correlated with SAT scores of 917 participants. The resulting correlation was.82 (.86 corrected for nonlinearity). Study 2 investigated the correlation between revised and recentered SAT scores and scores on the Raven's Advanced Progressive Matrices among 104 undergraduates. The resulting correlation was.483 (.72 corrected for restricted range). These studies indicate that the SAT is mainly a test of g. We provide equations for converting SAT scores to estimated IQs; such conversion could be useful for estimating premorbid IQ or conducting individual difference research with college students.     

The Swedish National Adult Reading Test (NART-SWE): a test of premorbid IQ

The purpose of this study was to construct a Swedish version of the National Adult Reading Test (NART-SWE), a test for assessment of premorbid IQ, and to investigate its validity and reliability on healthy controls and patients with mild Alzheimer's disease. As Swedish pronunciation rules are fixed, NART-SWE was constructed using loan words. NART-SWE has satisfactory psychometric properties: Inter-rater and retest reliability as well as internal consistency are very high. The NART-SWE demonstrates face validity. In addition, high correlation with IQ was obtained. A significant model emerged when using NART-SWE to predict IQ. Furthermore, no significant differences were observed when comparing performance for healthy controls' with that of patients with Alzheimer's disease on NART-SWE. It does appear that reading of irregular words is intact in mild Alzheimer's disease.     

Limitations to the validity of the Barona Regression Formula and similar demographically-based methods of estimating preinjury intellectual functioning

Neuropsychologists are frequently asked to determine the extent to which an individual displays compromised functioning as a consequence of alleged brain damage. Since IQ testing is commonplace, one method of evaluating consequences involves comparing postinjury IQ with an estimation of premorbid intelligence. Recognition that unaided clinical judgments are of questionable accuracy has prompted the development of actuarial formulae to estimate IQ based upon demographic information. One, the Barona Regression Formula (BRF), developed for the Wechsler Adult Intelligence Scale-Revised, has received recent endorsement in a widely read journal, which may lead to widespread use. Unfortunately, although the BRF appears to be empirically rigorous, and performs about as well as methods of this type could be expected to, it is insficiently valid to warrant more than extremely cautious employment in the individual case. The procedure shows greater promise with group data, but is less likely to be encountered in that usage. Reasons for viewing this and similar procedures as severely limited are discussed.     

IQ and the wealth of nations: How much reverse causality?

This paper uses data from 130 IQ test administrations worldwide and employs regression analysis to try to quantify the impact of living conditions on average IQ scores in nationally-representative samples. The study emphasizes the possible role of conditions at or near the test-takers' time of birth. The paper finds that the impact of living conditions is of much smaller magnitude than is suggested by just looking at correlations between average IQ scores and socioeconomic indicators. After controlling for test-takers' region of ancestry, the impact of parasitic diseases on average IQ is found to be statistically insignificant when test results from the Caribbean are included in the analysis. As far as IQ and the wealth of nations are concerned, causality thus appears to run mostly from the former to the latter. The test-takers' region of ancestry dominates the regression results. While differences in average scores worldwide can thus be plausibly viewed as being influenced by genetic differences across world regions, it is also possible that score differences are influenced by regional differences in culture that are independent of genetic factors. Differences in average IQ across world regions may change in the years ahead insofar as the strength of Flynn effects may not be uniform, but some regional differences in average g levels seem likely to continue indefinitely.     

The comparability of intelligence test results: Group- and individual-level comparisons of seven intelligence tests

A significant body of research has demonstrated that IQs obtained from different intelligence tests substantially correlate at the group level. Yet, there is minimal research investigating whether different intelligence tests yield comparable results for individuals. Examining this issue is paramount given that high-stakes decisions are based on individual test results. Consequently, we investigated whether seven current and widely used intelligence tests yielded comparable results for individuals between the ages of 4–20 years. Results mostly indicated substantial correlations between tests, although several significant mean differences at the group level were identified. Results associated with individual-level comparability indicated that the interpretation of exact IQ scores cannot be empirically supported, as the 95% confidence intervals could not be reliably replicated with different intelligence tests. Similar patterns also appeared for the individual-level comparability of nonverbal and verbal intelligence factor scores. Furthermore, the nominal level of intelligence systematically predicted IQ differences between tests, with above- and below-average IQ scores associated with larger differences as compared to average IQ scores. Analyses based on continuous data confirmed that differences appeared to increase toward the above-average IQ score range. These findings are critical as these are the ranges in which diagnostic questions most often arise in practice. Implications for test interpretation and test construction are discussed.     

Relation of Creativity to Fluid and Crystallized Intelligence

The threshold hypothesis regarding creativity and intelligence suggests that these two constructs are positively correlated except at the higher end of the IQ distribution, where they are unrelated. Much of the support for this hypothesis comes from comparisons of correlations within average and high‐IQ groups. However, a common methodological flaw in these comparisons is that the high IQ group is smaller in variance than the average IQ group. In the present study we equated variances for a better test of the threshold hypothesis. College students in two IQ groups completed tests of creativity and intelligence. IQ and creativity correlated at least as strongly in the high IQ group as in the average IQ group, generally failing to support the threshold hypothesis. However, breakdown of composite IQ into fluid and crystallized IQ indicated minimal support for the threshold hypothesis with crystallized IQ, but support for an inverse threshold effect with fluid IQ. Fluid IQ correlated significantly with creativity in the high IQ group but not in the average IQ group, and this pattern was corroborated by regression analyses. Possible explanations for the pattern of results are offered.     

A NOTE ON DIRECT RANGE RESTRICTION CORRECTIONS IN UTILITY ANALYSIS

Brogden's equations for employment test utility analysis have been used in conjunction with direct range restriction correction formulas, because the data used typically come from selected applicant (incumbent) samples. We show that the use of direct range restriction corrections in utility analysis is not needed. Identical results can be obtained using a simpler equation that employs a regression coefficient based on the employee (i.e., restricted or job incumbent) population. This utility estimation procedure, which does not employ range restriction corrections, is derived and discussed. We recommend that this new equation be used in the practice of selection utility analysis because it not only provides identical utility estimates to those obtained using current equations that employ direct range restriction correction formulas, but also is computationally simpler.     

IQ decline following early unilateral brain injury: a longitudinal study

We examine whether children with early unilateral brain injury show an IQ decline over the course of development. Fifteen brain injured children were administered an IQ test once before age 7 and again several years later. Post-7 IQ scores were significantly lower than pre-7 IQ scores. In addition, pre-7 IQ scores were lower for children with larger lesions, but children with smaller lesions and higher pre-7 IQ scores showed a greater IQ decline over time. These findings suggest that the cognitive outcomes of children with early lesions, particularly those with relatively small lesions, change over the course of development.     

Assessment of perception of morphed facial expressions using the Emotion Recognition Task: Normative data from healthy participants aged 8–75

The ability to recognize and label emotional facial expressions is an important aspect of social cognition. However, existing paradigms to examine this ability present only static facial expressions, suffer from ceiling effects or have limited or no norms. A computerized test, the Emotion Recognition Task (ERT), was developed to overcome these difficulties. In this study, we examined the effects of age, sex, and intellectual ability on emotion perception using the ERT. In this test, emotional facial expressions are presented as morphs gradually expressing one of the six basic emotions from neutral to four levels of intensity (40%, 60%, 80%, and 100%). The task was administered in 373 healthy participants aged 8–75. In children aged 8–17, only small developmental effects were found for the emotions anger and happiness, in contrast to adults who showed age‐related decline on anger, fear, happiness, and sadness. Sex differences were present predominantly in the adult participants. IQ only minimally affected the perception of disgust in the children, while years of education were correlated with all emotions but surprise and disgust in the adult participants. A regression‐based approach was adopted to present age‐ and education‐ or IQ‐adjusted normative data for use in clinical practice. Previous studies using the ERT have demonstrated selective impairments on specific emotions in a variety of psychiatric, neurologic, or neurodegenerative patient groups, making the ERT a valuable addition to existing paradigms for the assessment of emotion perception.     

The prediction of intelligence in preschool children using alternative models to regression

Statistical prediction of an outcome variable using multiple independent variables is a common practice in the social and behavioral sciences. For example, neuropsychologists are sometimes called upon to provide predictions of preinjury cognitive functioning for individuals who have suffered a traumatic brain injury. Typically, these predictions are made using standard multiple linear regression models with several demographic variables (e.g., gender, ethnicity, education level) as predictors. Prior research has shown conflicting evidence regarding the ability of such models to provide accurate predictions of outcome variables such as full-scale intelligence (FSIQ) test scores. The present study had two goals: (1) to demonstrate the utility of a set of alternative prediction methods that have been applied extensively in the natural sciences and business but have not been frequently explored in the social sciences and (2) to develop models that can be used to predict premorbid cognitive functioning in preschool children. Predictions of Stanford–Binet 5 FSIQ scores for preschool-aged children is used to compare the performance of a multiple regression model with several of these alternative methods. Results demonstrate that classification and regression treesprovided more accurate predictions of FSIQ scores than does the more traditional regression approach. Implications of these results are discussed.     

A systematic literature review of the average IQ of sub-Saharan Africans

On the basis of several reviews of the literature, Lynn [Lynn, R., (2006). Race differences in intelligence: An evolutionary analysis. Augusta, GA: Washington Summit Publishers.] and Lynn and Vanhanen [Lynn, R., & Vanhanen, T., (2006). IQ and global inequality. Augusta, GA: Washington Summit Publishers.] concluded that the average IQ of the Black population of sub-Saharan Africa lies below 70. In this paper, the authors systematically review published empirical data on the performance of Africans on the following IQ tests: Draw-A-Man (DAM) test, Kaufman-Assessment Battery for Children (K-ABC), the Wechsler scales (WAIS & WISC), and several other IQ tests (but not the Raven's tests). Inclusion and exclusion criteria are explicitly discussed. Results show that average IQ of Africans on these tests is approximately 82 when compared to UK norms. We provide estimates of the average IQ per country and estimates on the basis of alternative inclusion criteria. Our estimate of average IQ converges with the finding that national IQs of sub-Saharan African countries as predicted from several international studies of student achievement are around 82. It is suggested that this estimate should be considered in light of the Flynn Effect. It is concluded that more psychometric studies are needed to address the issue of measurement bias of western IQ tests for Africans.     

The association of childhood intelligence with mortality risk from adolescence to middle age: Findings from the Aberdeen Children of the 1950s cohort study

There is growing evidence that childhood IQ is inversely associated with mortality in later life. However, the specificity of this association in terms of causes of death, whether it is continuous over the whole range of IQ scores and whether it is the same according to age and sex is not clear. In a large cohort (N = 11,603) of a complete population of children born in one city in the UK in the early 1950s, IQ measured at age 7 years (using a routinely administered picture test) was found to be inversely associated with mortality between the ages of 15 and 57 years. For every 1 SD increase in IQ at 7, the all cause mortality hazard ratio was 0.79 (95% CI 0.73, 0.85). On adjustment for a range of perinatal factors, father's social class at birth, number of sibs in the household and childhood height and weight, this was attenuated slightly to 0.81 (0.74, 0.88). Almost identical associations of IQ with mortality were seen for men and women as well as at younger (15–39) and older (40+) ages. These associations were across the entire IQ range, although some of the high mortality in the lowest category of IQ (< 70) was accounted for by causes associated with congenital disorders. Overall, external causes of death showed the strongest association, with weaker associations being seen for cancer. Further work is required to understand the mechanisms whereby childhood IQ has such a robust association with mortality in later life.     

The determinants of parents' beliefs about the intelligence their children: A study from Hong Kong

One hundred and ninety‐three Hong Kong parents (mean age 42.2 years) were given a structured interview / questionnaire concerning their own and their children's self‐estimated overall and multiple intelligence. Previous research suggested that males tend to give higher overall “g” estimates to their children and themselves than do females, as well as higher scores on mathematical and spatial intelligence (Furnham, 2001). Further, studies in the West suggest that parents think their children are significantly brighter than they are and that their sons are brighter than their daughters. Estimates were lower than those found in Western populations but, even so, males rated their own mathematical and spatial intelligence higher than did females. Hong Kong Chinese parents did not think their sons were brighter than their daughters. The seven multiple intelligences factored into three clear factors for self and children, and regressions indicated that it was “academic” intelligence (verbal, mathematical, spatial) that was most “g” loaded. The child's age and the self‐rated overall IQ of both the parents were the best predictors of the child's overall estimated IQ. Less than a third of the parents had taken an IQ test or believed they measured IQ very well. Those who were more likely to be better educated, had taken an IQ test, and believed intelligence was inherited were more likely to award themselves higher overall IQ scores. Results are compared with the British studies in the same area.     

State preferences for the ACT versus SAT complicates inferences about SAT-derived state IQ estimates: A comment on Kanazawa (2006)

Kanazawa [Kanazawa, S. (2006). IQ and the wealth of states. Intelligence, 34, 593–600.] offered estimates of state IQ derived from SAT data. The purpose of this commentary is to argue that state preferences for the use of the ACT versus the SAT create biased estimates of SAT-derived state IQ for states where the ACT is more frequently used than the SAT. This error can be reduced by using both ACT and SAT data to estimate state IQ. An IQ estimate based on a ACT-SAT composite and a NAEP-derived state IQ estimate were compared as predictors of three wealth variables. Both IQ estimates cause one to conclude that states with higher mean IQ have larger gross state product per capita, higher median incomes, and a lower percentage of their population in poverty.