Sex differences in verbal reasoning are mediated by sex differences in spatial ability

Transcription

1 1 Title Sex differences in verbal reasoning are mediated by sex differences in spatial ability Authors Affiliation Roberto Colom Mª José Contreras Isabel Arend Oscar García-Leal José Santacreu Facultad de Psicología. Universidad Autónoma de Madrid Madrid (Spain) Corresponding author + Roberto Colom Facultad de Psicología Universidad Autónoma de Madrid Madrid (Spain) roberto.colom@uam.es IN PRESS: The Psychological Record + Ac knowledgementthis researc h was supported by the projec t AENA-UAM/

2 2 Abstract Several meta-analyses have shown that males outperform females in overall spatial ability, while females outperform males in some verbal ability tests, but not in others. The present article measures sex differences in two computerized tests, one thought to reflect verbal reasoning and one thought to reflect dynamic spatial performance. The sample comprised 1,593 university graduates (794 females and 799 males). Results show that males outperform females in both tests. However, sex differences in verbal reasoning turn to be nonsignificant when sex differences in dynamic spatial performance are statistically removed. The finding is interpreted from the previously demonstrated fact that the verbal reasoning test requires spatial processing. The result raise doubts about the common practice of evaluating sex differences in cognitive abilities from the tests superficial characteristics or its information content. The interpretation of the observed findings strongly requires the analysis of the tests cognitive requirements. Keywords: Sex differences, Verbal reasoning, Verbal ability, Spatial ability, Cognitive abilities, Human information processing

3 3 INTRODUCTION There are hundreds of studies about sex differences in cognitive abilities (see Halpern, 2000, for a comprehensive review). The huge available number of databases facilitated the publication of several key meta-analyses from which some robust conclusions have been extracted. Hyde (1981) published the first meta-analysis from the data summarized by Maccoby & Jacklin (1974) in their classic book The psychology of sex differences. The results showed that boys outperform girls in overall spatial and quantitative abilities, while the later outperform the former in overall verbal ability. Some years later, Hyde & Lynn (1988) found in their meta-analysis that females outperform males in overall verbal ability. The meta-analysis reported by Hyde, Fennema, and Lamon (1990) found a male advantage in overall quantitative ability, but those researchers noted that quantitative items are frequently expressed spatially. The meta-analysis by Linn & Petersen (1985) reported a male advantage in spatial rotation, spatial relations, and visualization. Voyer, Voyer, & Bryden (1995) have replicated those findings. Finally, Feingold (1988) and Lynn (1999) observed a male advantage in reasoning ability. Therefore, previous research shows that the greater male advantage can be found in overall spatial ability (Halpern, 2000; Hedges & Nowell, 1995). Some researchers have investigated sex differences in so-called dynamic spatial tests (Law, Pellegrino, & Hunt, 1993; Sacuzzo, Craig, Johnson, & Larson, 1996; Contreras, Colom, Shih, Álava, & Santacreu, 2001; Colom, Contreras, Botella, & Santacreu, 2002). Hunt, Pellegrino, Frick, Farr, & Alderton (1988) reported a seminal study about static and dynamic spatial abilities. Static

4 4 refers to spatial factors measured by printed tests of visualization or spatial relations (Lohman, 2000). Dynamic spatial tasks measure the ability to perceive and extrapolate real motion, to predict trajectories of moving objects, and to estimate arrival times of two or more objects. Those researchers supported the view that dynamic spatial performance should be preferably measured by computerized tests (Law, Pellegrino, Mitchell, Fischer, McDonald, & Hunt, 1993; Law, Pellegrino, & Hunt, 1993; Pellegrino & Hunt, 1989; Pellegrino, Hunt, Abate, & Farr, 1987). Contreras, Colom, et al. (2001) have assessed six hundred university graduates (half of them females) through two dynamic spatial tests. The computerized tests require the simultaneous orientation of two moving points to a given destination. Males outperformed females even when both come from the same or different educational branches (humanities, social sciences, natural sciences, and engineering). Thus, for instance, the scores of females graduated in engineering were lower than the scores of males graduated in humanities. Therefore, sex differences in dynamic spatial tests were not conditioned by previous educational differences. On the other hand, there are contradictory findings about sex differences in verbal ability. Females outperform males in verbal fluency (Hines, 1990), synonym generation (Halpern & Wright, 1996), or reading comprehension (Hedges & Nowell, 1995). However, males outperform females in verbal analogies (Lim, 1994). Sex differences in verbal ability measures are not always favorable to females. Nevertheless, Colom, Contreras, Arend, Botella, & Santacreu (2002) have demonstrated that performance in a test of verbal

5 5 reasoning based on linear syllogisms or three-term series (John is better than Peter : Peter is better than Paul :: Who is worse?) is accurately predicted from a model of human information processing based on the mental transformation of the verbal information into a mental spatial diagram or a mental model (DeSoto, London, & Handel, 1965; Johnson-Laird, 1999; Sternberg, 1980; see also Arend, Colom, Botella, Contreras, Rubio, & Santacreu, in press). Thus, the demonstrated male advantage in overall spatial processing is a good candidate to (partly) account for their better performance in verbal reasoning tests. Taking this possibility into account, the present study predicts that the male advantage in verbal reasoning will diminish if sex differences in spatial processing are statistically removed. There are some previous studies that can be cited as supportive of this prediction. Abad, Colom, Rebollo, & Escorial (in press) have demonstrated, through DIF (Differential Item Functioning) analysis (see Holland & Wainer, 1993; Thissen, 1991), that several items from the Advanced Progressive Matrices Test are biased against females. The bias derives from the figurative content of the Progressive Matrices Test. The results observed by those researchers suggest that female performance on the Progressive Matrices Test could require reasoning ability but also spatial ability. Female lower spatial ability could depress their performance in measures that (presumably) rely only in abstract reasoning (see also Lim, 1994). Moreover, Colom, Escorial, & Rebollo (2002) have analyzed sex differences in the Advanced Progressive Matrices Test. Those researchers assessed spatial ability through the mental rotation subtests from the Primary Mental Abilities Battery. The male advantage

6 6 in the Raven Matrices Test turn to be non-significant when sex differences in mental rotation were statistically removed. Those studies suggest that the average lower females scores in overall spatial ability could diminish their performance in tasks that are verbal at the surface, but that in fact require spatial processing. Linear syllogisms or threeterm series are especially appropriate to test this prediction, given that previous findings indicate that those problems require spatial processing (Sternberg, 1980; Colom, Contreras, et al., 2002; Arend, Colom, et al., in press). The present study assesses a broad sample of males and females through a verbal reasoning test (three-term series or linear syllogisms) and a dynamic spatial test. Sex differences in both tests are first evaluated. Second, the prediction that sex differences in verbal reasoning will diminish when sex differences in spatial ability are statistically removed was tested.

7 7 METHOD Participants The sample comprised 1,593 university graduate applicants for an Air Traffic Control training course. 794 were females and 799 were males. The mean age for females was (SD = 4.16) and the mean age for males was (SD = 4.86). Although we must acknowledge that the sample is not representative of the population, the important point is that this is true both for males and females. Moreover, those graduates came from several academic branches: engineering, natural sciences, social sciences, and humanities. Measures and procedures Participants completed a computerized test of verbal reasoning and a computerized test of dynamic spatial performance. The verbal reasoning test consisted of 32 three-term series. Those series comprise two premises. Each premise describes the relationship between two of three terms (A-B-C). One of the terms (B) overlaps between the premises. This overlap allows the establishment of the relation between the pair of terms not presented in a single premise. For example, John (A) is more able than Peter (B) : Peter (B) is more able than Paul (C) :: Who is duller? Each premise involves a relation between two terms (A> B : B > C). The person must combine the information from the two premises in order to make an inference about the relationship between A and C. This basic structure allows the construction of 32 syllogisms, combining the relation between the terms on the two premises and the localization of the response. Sixteen syllogisms were characterized by

8 8 positive comparative forms (more able than) and the remaining were characterized by negative equatives (not more able than). Each item was presented in a sequence: first premise (John is more able than Peter), second premise (Peter is more able than Paul), question (Who is duller?), and response (John-Peter-Paul). The participant press the mouse within a square in which the to be processed information is presented. The participant is required to code the premises and respond to the question accurately, but as soon as possible. The number of hits was obtained as the participant score. The test reliability was.92 (Cronbach s alpha). The dynamic spatial test (SODT-R) requires the simultaneous orientation of two moving points to a given destination. The destination changes from trial to trial and the two moving points could come from the North, the East, or the West of the computer screen. The participant must direct the moving points through a box with two arrows linked to each moving point. One arrow moves the point in a given direction, while the other arrow moves it in the opposite direction (Figure 1; see more details in Colom, Contreras, Shih, & Santacreu, 2003). The test consists of 10 trials. Grade deviation between the orientation estimated by the participant and the correct orientation was obtained as the final score (higher scores reflect worse performance). The test reliability was.88 (Cronbach s alpha). PLEASE INSERT FIGURE 1 ABOUT HERE

9 9 The participants were assessed in a facility comprising 60 testing stations. Each station was isolated to preserve the participant of being disturbed during the session. RESULTS Table 1 shows the descriptive statistics for males and females on the verbal reasoning and dynamic spatial tests. Table 1 also shows the average sex difference in d units. PLEASE INSERT TABLE 1 ABOUT HERE The effect size for verbal reasoning is much lower than for spatial performance. While the former can be considered a small effect size, the later is clearly very high. However, taking into account the sample size, an effect size of.16 must be considered of high practical relevance (Cohen, 1988). The statistical significance of the difference between males and females was tested by analysis of variance. The sex difference in the verbal reasoning test was significant [F (1, 1592) = 9.568, p <.01] and the sex difference in the dynamic spatial test was also significant [F (1, 1592) = , p <.01]. Therefore, males outperform females in both tests. The next step was a test of the study s basic prediction: do sex differences in verbal reasoning diminish when sex differences in spatial ability are statistically removed? One analysis of variance was computed where the dependent variable was the scores in the verbal reasoning test, the

10 10 independent variable was sex, and the covariate was the scores in the dynamic spatial test. Sex differences in the verbal reasoning test were not significant when sex differences in spatial processing were statistically controlled [F (1, 1592) = 1.076, p =.300]. Thus, the prediction stated is correct. Because males outperform females in overall spatial processing, differences in a verbal test requiring spatial processing favour males. However, those sex differences turn to be non-significant when sex differences in spatial processing are removed. 1 Moreover, the Pearson correlation between verbal reasoning and spatial performance for the entire sample was.22 (p<.01), for males it was.17 (p<.01), and for females it was.24 (p<.01), which suggests that females performance could rely more heavily in spatial processing for both tests. 1 One reviewer suggested to c arry out a moderator analysis. Although interesting this kind of analysis is beyond the sc ope of the present researc h.

11 11 DISCUSION Halpern (2000) has pointed out that the classification of cognitive tests according to their reasoning, verbal, or spatial appearance could be an oversimplification. Jensen (1998) noted that the superficial characteristics of the tests do not always reflect the required cognitive ability. We think that those cautions apply to the results observed in the present study. Males outperform females in both the verbal reasoning and dynamic spatial tests. It can be considered that the male advantage in the verbal reasoning test contradicts previous findings indicating that females outperform males in verbal tests. However, the present study predicted that if spatial processing is required to solve the items from the verbal reasoning test, a male advantage could be expected because males outperform females in overall spatial ability. Thus, males will obtain extra credit to solve verbal problems requiring spatial processing from their higher spatial ability (DeSoto, London, & Handel, 1965; Sternberg, 1980). Colom, Contreras, et al. (2002) have demonstrated that a theoretical model of human information processing based on the prediction that the resolution of linear syllogisms require spatial processing (the so-called spatial model) largely predicts performance (see also Arend, Colom, et al., in press). Thus, although the three-term series are expressed through a verbal content (superficial appearance of the items), information processing requires spatial ability (cognitive requirements of the items). The distinction between superficial appearance and cognitive requirements could help to explain the observed male advantage. Although

12 12 males outperform females in both the verbal reasoning and dynamic spatial tests, the sex difference in the test superficially verbal turn to be non-significant when the sex difference in the dynamic spatial test is statistically removed. Note that this is not to say that only spatial processing is affecting such differences. The findings discussed in the present study prevent against the frequent practice of evaluate sex differences in a given cognitive ability through a single test. Colom & García-López (2002) have demonstrated that this practice can produce very different conclusions. Those researchers measured sex differences in fluid intelligence through a test based on letters (the inductive reasoning test from the Primary Mental Abilities Battery) and through a test based on figures (the Advanced Progressive Matrices Test). Females outperformed males in the fluid test based on letters, while males outperformed females in the fluid test based on figures. The present study adds another prevention that could be considered as crucial: the evaluation of sex differences in a given cognitive ability must rely neither in a single test nor in the test superficial appearance. The cognitive (information processing) requirements imposed by a given test must be investigated before using it to evaluate sex differences in the main cognitive abilities (Halpern, 2000). Unfortunately, those cautions are frequently forgotten. REFERENCES Abad, F.J., Colom, R., Rebollo, I., & Escorial, S. (in press). Sex differential item functioning in the Raven s Advanced Progressive Matrices: Evidence for bias. Personality and Individual Differences.

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16 16 TABLE 1 Descriptive statistics of males and females. The mean difference in standard deviation units (d) is also shown Tests Males Females Mean SD Skew Kurtosis Mean SD Skew Kurtosis Mean difference (d) Linguistic reasoning Dynamic spatial performance

17 Figure 1 Spatial Orientation Dynamic Test-Revised (SODT-R). The participant must simultaneously direct the two moving points to the destination displayed at the bottom of the computer screen. The participant must use the box displayed at the top of the computer screen 17