The Paradox of Sex Differences in Intelligence – Updated

In our blog on sex differences in general and specific abilities we suggested that these differences did not disappear, or show a decline because in modern Western societies opportunities for men and women became more equal. This brief update was motivated by two reasons (1) sex differences in general and specific abilities have an extreme social and political impact sometimes interfering with facts and (2) new research evidence. 

The new data are on sex differences in math ability. The authors of the most comprehensive analysis on sex-related differences in science, math and verbal test performance, Wai et al. (2010), who summarized data from 1981 to 2010, have recently provided an update for the period from 2011 – 2015 (Makel et al., 2016). Just a brief recap of the already reported findings: although sex differences at the average have largely disappeared, performance differences in the extreme tails remain or have even increased (0.01% right tail, or perfect SAT-math score). The new data updated male-female ability ratios in the extreme right tail of math and verbal domains for the last five years. Furthermore, the authors replicated male-female ability ratios in a sample of students from India participating in a talent search.

Figure 1. Male to female ratios for the 0.01% high scorers on SAT – math, ACT – math, EXPLORE – math (EXPLORE for the younger elementary aged students as part of Duke TIP), ACT – science and EXPLORE – science, for the period 2006 – 2010 and the added period of 2011 – 2015.

As revealed in Figure 1, although the male advantage in math test performance still prevails, the ratio showed a decline in the 2011 – 2015 period (SAT and ACT). On the other hand, for the younger generation (EXPLORE) there were no changes for math male to female ratios, being similar to science ratios that also remained stable. The male to female ratios in the extreme-right tail of Indian participants showed the same trend: math (7.8) and a smaller male advantage in science (4.5).

Figure 2. Male to female ratios for the 0.01% high scorers on SAT – verbal, ACT – English, EXPLORE – English, ACT – Reading and EXPLORE – Reading, for the period 2006 – 2010 and the added period of 2011 – 2015.

As can be seen in Figure 2, females showed an advantage over males in verbal domains, which at least for the extreme performers (0.01%) remained rather stable. The same trend was observed for the Indian sample. Females showed a clear performance advantage in the extreme right tail of the English test (0.62), which increased to 0.35 after correction for participation differences.

A widely accepted explanation for the observed sex differences is the gender stratification hypothesis by Else-Quest (Else-Quest et al., 2010). The essence of the theory is that sex-related differences in performance are the result of a lack of societal opportunities. The differences are becoming smaller as social beliefs regarding male-dominated domains change and opportunities for men and women become more equal. As stressed by Stoet (Stoet et al., 2016), the theory faces some problems. For instance, how to explain that in economically developed and more gender equal countries, the overall level of math anxiety is lower than in less developed countries, whereas the sex difference in math anxiety is much higher as compared to less developed countries. Another surprising finding was that, although in more developed countries more mothers work in so-called science and math jobs, these parents valued mathematical competence more in their sons than in their daughters.

Math anxiety is a negative emotional reaction to situations involving mathematical problem solving (Young et al., 2012). It has a negative effect on mathematical performance and as shown in several neuroimaging studies, it also has a neural signature (Lions and Bylock, 2012; Supekar et al., 2015). The brain regions that are involved in this reaction are associated with visceral threat detection, and often the experience of pain itself (bilateral dorso-posterior insula; Lions and Bylock, 2012), as well as parts of the amygdala related to the processing of negative emotions (Supekar et al., 2015; Young, et al., 2012).

The explanations provided for the finding that sex differences in math anxiety are larger in more gender equal countries were power distance and a “luxury hypothesis” (Stoet et al, 2016). Power distance is related to the between-strata social comparison. In more gender equal countries the distance is small and there is much more comparison between boys and girls than in countries with low gender equality. However, the study by Stoet and colleagues (based on 761,655 15-year old students across 68 nations – PISA) did not confirm this hypothesis. Increased opportunity for between gender comparison (mixed-sex versus single-sex schools) had no influence on math anxiety. The luxury hypothesis assumes that when basic needs are fulfilled (developed countries) the interest for math attitude and affect are more prevalent. However, the hypothesis cannot explain the finding that in more gender equal countries the overall levels of math anxiety of both sexes are lower. The authors concluded “Our findings do not provide support for a number of key predictions of the gender-stratification hypothesis” (Stoet et al., 2016, p. 18). The authors proposed a different theory suggesting that development enables individuals to choose their occupation based more on intrinsic interest and less on financial drives.

Yet another unexplained paradox.

Similar to a more autobiographic one that I am still ruminating on. My daughter studied physics at Durham University UK, defending her PhD thesis at Imperial college London. She published several papers, also in Nature, was offered a postdoc fellowship at Cambridge University, which she turned down for a fulltime housewife position.

References

Else-Quest, N. M., Hyde, J. S., & Linn, M. C. (2010). Cross-national patterns of gender differences in mathematics: A meta-analysis. Psychological Bulletin, 136(1), 103–127. https://doi.org/10.1037/a0018053

Lyons, I. M., & Beilock, S. L. (2012). When Math Hurts: Math Anxiety Predicts Pain Network Activation in Anticipation of Doing Math. PLoS ONE, 7(10), e48076. https://doi.org/10.1371/journal.pone.0048076

Makel, M. C., Wai, J., Peairs, K., & Putallaz, M. (2016). Sex differences in the right tail of cognitive abilities: An update and cross cultural extension. Intelligence, 59, 8–15. https://doi.org/10.1016/j.intell.2016.09.003

Stoet, G., Bailey, D. H., Moore, A. M., & Geary, D. C. (2016). Countries with Higher Levels of Gender Equality Show Larger National Sex Differences in Mathematics Anxiety and Relatively Lower Parental Mathematics Valuation for Girls. PLOS ONE, 11(4), e0153857. https://doi.org/10.1371/journal.pone.0153857

Supekar, K., Iuculano, T., Chen, L., & Menon, V. (2015). Remediation of Childhood Math Anxiety and Associated Neural Circuits through Cognitive Tutoring. Journal of Neuroscience, 35(36), 12574–12583. https://doi.org/10.1523/JNEUROSCI.0786-15.2015

Wai, J., Cacchio, M., Putallaz, M., & Makel, M. C. (2010). Sex differences in the right tail of cognitive abilities: A 30year examination. Intelligence, 38(4), 412–423. https://doi.org/10.1016/j.intell.2010.04.006

Young, C. B., Wu, S. S., & Menon, V. (2012). The Neurodevelopmental Basis of Math Anxiety. Psychological Science, 23(5), 492–501. https://doi.org/10.1177/0956797611429134