Francisco J. Abad

Complex span tasks, simple span tasks, and cognitive abilities: A reanalysis of key studies

There is great interest in the relationships between memory span tasks and cognitive abilities. However, the causes underlying their correlation remain unknown. In the present article, five key data sets were reanalyzed according to two criteria: They must consider complex span tasks (so-called working memory [WM] tasks) and simple span tasks (so-called short-term memory [STM] tasks), and they must comprise cognitive ability measures. The obtained results offer several points of interest. First, memory span tasks should be conceived from a hierarchical perspective: They comprise both general and specific components. Second, the general component explains about four times the variance explained by the specific components. Third, STM and WM measures are closely related. Fourth, STM and WM measures share the same common variance with cognitive abilities. Finally, the strong relationship usually found between memory span tasks and cognitive abilities could be tentatively interpreted by the component shared by STM and WM—namely, the capacity for temporarily preserving a reliable memory representation of any given information.

A new look at Horn's parallel analysis with ordinal variables.

Previous research evaluating the performance of Horns parallel analysis (PA) factor retention method with ordinal variables has produced unexpected findings. Specifically, PA with Pearson correlations has performed as well as or better than PA with the more theoretically appropriate polychoric correlations. Seeking to clarify these findings, the current study employed a more comprehensive simulation study that included the systematic manipulation of 7 factors related to the data (sample size, factor loading, number of variables per factor, number of factors, factor correlation, number of response categories, and skewness) as well as 3 factors related to the PA method (type of correlation matrix, extraction method, and eigenvalue percentile). The results from the simulation study show that PA with either Pearson or polychoric correlations is particularly sensitive to the sample size, factor loadings, number of variables per factor, and factor correlations. However, whereas PA with polychorics is relatively robust to the skewness of the ordinal variables, PA with Pearson correlations frequently retains difficulty factors and is generally inaccurate with large levels of skewness. In light of these findings, we recommend the use of PA with polychoric correlations for the dimensionality assessment of ordinal-level data.

Negligible sex differences in general intelligence

Abstract The general factor, g , can be extracted from a correlation matrix of a battery of mental ability tests. g is common to all mental abilities. A key question in the research on cognitive sex differences is whether, on average, females and males differ in g . This question is technically the most difficult to answer and has been the least investigated. Cognitive batteries were applied in the present study to independent samples totaling 10,475 adult subjects (4,256 females and 6,219 males). The scores were factor-analyzed by sex to obtain separate g factors. The congruence coefficients ( r c ) suggested a near identity of these factors. Then, three methods were used to know if the standardized sex differences ( ds ) are explained by g : (1) the method of correlated vectors; (2) the sex loading in g was computed including the point-biserial correlation between sex and each of the subtests in the full matrix of subtest intercorrelations for factor analysis; and (3) the correlation between sex and g factor scores. The results suggest a negligible sex difference in g . The present study includes the largest sample on which a sex difference in g has ever been tested. The findings are consistent with those using quite different test batteries and subject samples.

Age dedifferentiation hypothesis: Evidence from the WAIS III

There is a renewed interest in the so-called age differentiation hypothesis—and the related age dedifferentiation hypothesis. The former states a reduction in the size of g at the first stage of life until early maturity. The latter hypothesized an increase in the importance of g at late adulthood and a decrease in the number of factors. The Spanish standardization of the WAIS-III (N=1369) was used in the present study to test the age dedifferentiation hypothesis. The results show no changes in the percentage of variance accounted for by g and four group factors (Verbal, Perceptual Organization, Working Memory, and Processing Speed) when the restriction of range is controlled. The ageindifferentiation hypothesis, as well as the anatomical metaphor, is proposed as a more fine-grained perspective to look at the development of the structure of cognitive abilities along the life span. D 2002 Elsevier Science Inc. All rights reserved.

Neuroanatomic overlap between intelligence and cognitive factors: morphometry methods provide support for the key role of the frontal lobes.

Evidence from neuroimaging studies suggests that intelligence differences may be supported by a parieto-frontal network. Research shows that this network is also relevant for cognitive functions such as working memory and attention. However, previous studies have not explicitly analyzed the commonality of brain areas between a broad array of intelligence factors and cognitive functions tested in the same sample. Here fluid, crystallized, and spatial intelligence, along with working memory, executive updating, attention, and processing speed were each measured by three diverse tests or tasks. These twenty-one measures were completed by a group of one hundred and four healthy young adults. Three cortical measures (cortical gray matter volume, cortical surface area, and cortical thickness) were regressed against psychological latent scores obtained from a confirmatory factor analysis for removing test and task specific variance. For cortical gray matter volume and cortical surface area, the main overlapping clusters were observed in the middle frontal gyrus and involved fluid intelligence and working memory. Crystallized intelligence showed an overlapping cluster with fluid intelligence and working memory in the middle frontal gyrus. The inferior frontal gyrus showed overlap for crystallized intelligence, spatial intelligence, attention, and processing speed. The fusiform gyrus in temporal cortex showed overlap for spatial intelligence and attention. Parietal and occipital areas did not show any overlap across intelligence and cognitive factors. Taken together, these findings underscore that structural features of gray matter in the frontal lobes support those aspects of intelligence related to basic cognitive processes.

Intelligence differentiation in adult samples

There is a renewed interest in the so-called differentiation theory. This theory states: the higher the level of g, the less the amount of g variance in any particular cognitive test. The implication of the differentiation theory for the scientific concept of intelligence is noteworthy: g could be more germane for low-ability than for high-ability people. A first battery of cognitive tests was applied to a sample of 3430 participants (mean age=23.12 years). The sample of the Spanish standardization of the WAIS-III was also analyzed (823 participants with a mean age=34.41 years). The methodology of Deary et al. [Intelligence 23 (1996) 105] was used for generating fine-grained low- and high-ability groups. The percentage of variance explained by g was computed for low- and high-ability groups, respectively: the mean percentages were 45.85 and 43.96 in the first cognitive battery, and 49.03 and 36.67 in the WAIS-III. These results support the differentiation of intelligence across the range of ability. However, a sample effect is observed: WAIS-III results are more supportive of the differentiation theory. This evidence suggests that ability differentiation could be related to educational differences. D 2003 Elsevier Science Inc. All rights reserved.

Education, Wechsler's Full Scale IQ, and g

The scientific construct of general intelligence (g) rests on the correlations among test scores, while IQ rests on the summation of standardized scores. Although IQ is usually considered a fine-grained proxy measure of general intelligence, IQ is actually an arbitrary variable (intelligence in general) not a scientific construct (general intelligence). This study examines the question of whether or not average Full Scale IQ (FSIQ) differences between groups that differ in their academic level can be attributed to g, because IQ results from g plus a mixture of specific cognitive abilities and skills. The Spanish standardization sample of the Wechsler Adult Intelligence Scale (WAIS-III) is analyzed. The sample comprised 703 females and 666 men aged 15–94 drawn as representative of the population in forms of educational level and geographical location. The results support the conclusion that the Wechsler FSIQ does not directly or exclusively measure g across the full range of the population distribution of intelligence. There is no significant association between the scientific construct of general intelligence (g) and the differences in intelligence in general (IQ) assessed by the WAIS-III. Some theoretical conclusions are stated as consequence of this lack of association. D 2002 Elsevier Science Inc. All rights reserved.

Generational changes on the draw-a-man test: a comparison of Brazilian urban and rural children tested in 1930, 2002 and 2004.

Although gains in generational intelligence test scores have been widely demonstrated around the world, researchers still do not know what has caused them. The cognitive stimulation and nutritional hypotheses summarize the several diverse potential causes that have been considered. This article analyses data for a sample of 499 children tested in 1930 and one equivalent sample of 710 children tested 72 years later, the largest gap ever considered. Both samples comprised children aged between 7 and 11 who were assessed by the Draw-a-Man test in the city of Belo Horizonte, Brazil. Further, one additional sample of 132 children was assessed in 2004 in a rural area very similar in several diverse factors to the 1930 urban sample. The results are consistent with both the cognitive stimulation and the nutritional hypotheses.

Sex differential item functioning in the Raven's Advanced Progressive Matrices: evidence for bias

There are no sex differences in general intelligence or g. The Progressive Matrices (PM) Test is one of the best estimates of g. Males outperform females in the PM Test. Colom and Garcia-Lopez (2002) demonstrated that the information content has a role in the estimates of sex differences in general intelligence. The PM test is based on abstract figures and males outperform females in spatial tests. The present study administered the Advanced Progressive Matrices Test (APM) to a sample of 1970 applicants to a private University (1069 males and 901 females). It is predicted that there are several items biased against female performance, by virtue of their visuo-spatial nature. A double methodology is used. First, confirmatory factor analysis techniques are used to contrast one and two factor solutions. Second, Differential Item Functioning (DIF) methods are used to investigate sex DIF in the APM. The results show that although there are several biased items, the male advantage still remains. However, the assumptions of the DIF analysis could help to explain the observed results.

Exploratory factor analysis in validation studies: uses and recommendations

BACKGROUND The Exploratory Factor Analysis (EFA) procedure is one of the most commonly used in social and behavioral sciences. However, it is also one of the most criticized due to the poor management researchers usually display. The main goal is to examine the relationship between practices usually considered more appropriate and actual decisions made by researchers. METHOD The use of exploratory factor analysis is examined in 117 papers published between 2011 and 2012 in 3 Spanish psychological journals with the highest impact within the previous five years. RESULTS RESULTS show significant rates of questionable decisions in conducting EFA, based on unjustified or mistaken decisions regarding the method of extraction, retention, and rotation of factors. CONCLUSIONS Overall, the current review provides support for some improvement guidelines regarding how to apply and report an EFA.