Group Differences in IQ: Comparisons Between Men And Women

COMPARISONS BETWEEN MEN AND WOMEN

With these preliminary points now established, we’re ready for the data—starting with the difference between men and women. Of course, men and women do differ in some ways. For example, men tend to be more physically aggressive than women; women, in contrast, rely on social aggression (gossiping, or ostracizing) more than men do. But men and women are also alike in many ways—and so, as just one illustration, evidence makes it clear that there’s virtually no difference between men and women in their effectiveness as leaders or their competitiveness as negotiators (J. Hyde & Linn, 2006).

What about intellectual abilities? Overall, neither sex is more intelligent than the other; and there’s no reliable difference between men and women in their IQ scores (e.g., Held, Alderton, Foley, & Segall, 1993; R. Lynn, 1994; although see N. Brody, 1992). We do detect differences, though, when we consider more specialized abilities. On average, men do better on certain tests designed to measure visuospatial abilities, such as tests requiring mental rotation (Figure 11.23). Men also do better on tasks that require them to navigate through a virtual (computerized) three-dimensional environ-ment (like the fictional worlds one must “travel through” in many computer games; Halpern, Benbow, Geary, Gur, Hyde et al., 2007). Women, for their part, on average do better on certain verbal tasks—especially tasks that require clear and fluent writing (Halpern, 1992, 2000; Halpern et al., 2007; L. Levine et al., 1999).

These differences are easily documented in the laboratory; but men and women also differ in their intellectual achievement outside of the lab, and the interpretation of this point has been a matter of controversy. To understand the debate, let’s start with the fact that many studies have documented differences between men and women in educational achievement—a so-called gender gap. One study examined the test scores for 15-year-olds in 41 different countries (Machin & Pekkarinen, 2008). In every country, girls outscored boys in tests of reading; in most countries, boys outscored girls in tests of mathematics. The data also showed that in both reading and mathematics, scores for boys were more variable than scores for girls; more boys than girls were likely to achieve scores rather distant from (above or below) the average for their sex (W. Johnson, Carothers, & Deary, 2008).

Another study compared the SAT scores of 40,000 American high-school students. The study showed that men (on average) did better than women on the math portion of the test, even when the investigators limited their comparison to men and women who had taken exactly the same high-school math courses and had expressed the same degree of interest in mathematics (Benbow, 1988; Benbow, Lubinski, Shea, & Eftekhari-Sanjani, 2000; for related data, see Halpern et al., 2007).

Other considerations, however, complicate the comparison between the sexes. As one concern, we probably shouldn’t be comparing men and women in terms of math performance overall, because the gender comparison may depend on what type of math we’re considering. For example, the advantage for men seems clearer for tests that showcase spatial relations or geometry (Crawford & Chaffin, 1997; Halpern et al., 2007; J. Hyde, 2005); for tests emphasizing computation, the advantage goes to women (J. Hyde & Linn, 2006).

In addition, some measures don’t show women falling behind in mathematics. For example, National Science Foundation data indicate that men and women are equally likely to take calculus in high school, and it’s the women who get better grades (A. Gallagher & Kaufman, 2005). Similarly, America’s No Child Left Behind (NCLB) legislation requires states to assess student progress annually. A 2008 report on these assessments finds no difference between male and female high-school students in their average level of math achievement, although the scores for males continue to be somewhat more variable than the scores for females—so that males are more likely than females to obtain scores well below or well above the mean (J. Hyde, Lindberg, Linn, Ellis, & Williams, 2008; W. Johnson et al., 2008).

What about performance beyond high school? In college, men and women get equal math grades (Bridgeman & Lewis, 1996), even when we match their math classes for difficulty. Assessments of understanding of mathematical concepts in college courses likewise show no difference between the sexes (J. Hyde & Linn, 2006).

What lies behind all of these findings? For those studies that do detect sex differences in educational performance, what’s the cause? And why is it that, in the laboratory, men consistently have an advantage in visuospatial reasoning? Some authors have suggested biological explanations for these facts, often pointing to a possible link between spatial abilities and the male sex hormone testosterone. In one study, for example, males who produced abnormally low levels of testosterone showed impairments in spatial reasoning (Hier & Crowley, 1982); in another study, older males (aged 60–75) showed dramatic improvements in spatial reasoning after receiv-ing testosterone supplements (Cherrier et al., 2001; Janowsky, Oviatt, & Orwoll, 1994; also see Van Goozen, Cohen-Kettenis, Gooren, Frijda, & Can de Poll, 1995). But on the other hand, several studies have failed to confirm these hormonal effects on visu-ospatial performance, so any conclusions about this point must be tentative (e.g., Halari et al., 2005; Hines et al., 2003; Moffat & Hampson, 1996; also see Halpern, 2000; N. Newcombe, 2007; Spelke, 2005).

A different hypothesis focuses on cultural influences—including the important observation that in most Western cultures, young boys receive much more support and encouragement than young girls do for work in mathematics (Figure 11.24). Indeed, many people (including parents and teachers) seem to believe that women are ill suited for math and expect women not to do well in this domain (Halpern, 1992). Thus, parents expect their sons to do better in math courses than their daughters do (Frome & Eccles, 1998) and often attribute their sons’ success in math to ability while attributing their daughter ’s success in math to hard work (Parsons, Adler, & Kaczala, 1982). Even young children endorse these stereotypes (C. Steele, 2003) and, by middle adolescence, girls seem to receive less support from their peers for science- and math-related activities than boys do (Stake & Nickens, 2005) .

Do these social factors influence how children behave and what they achieve? Studies show that women perform less well on some math tests if they’re asked, at the start of the test, simply to record their gender on the test form. Presumably, this serves to prime the relevant stereotype, and this undermines performance (Ambady, Shih, Kim, & Pittinsky, 2001; we’ll go into greater detail about “stereotype threat” shortly). Similarly, sex differences in test scores are powerfully influenced by factors in the context that shape the test takers’ expectations. In one study, male and female college students all took a math test. Half of the students were told that this test had shown sex differences in the past; in this group, male students outperformed the females. The other half of the students were told that the test had been shown in the past to be gender fair; in this group, there was no sex difference in performance (R . Brown & Josephs, 1999; Crawford & Chaffin, 1997; Halpern et al., 2007).

Hypotheses emphasizing the role of experience and encouragement find further support in the fact that visuospatial skills can be markedly improved through practice—a point that has been documented in a wide range of studies (Halpern et al., 2007). In one experiment, male and female college students practiced playing an action video game (Medal of Honor: Pacific Assault) for a total of 10 hours. This practice improved the spatial skills of all participants, but the improvement was greater in women and led to a clear reduction in the difference between the sexes (Feng, Spence, & Pratt, 2007).

Indeed, in light of the studies showing the positive influence of instruction, experi-ence, and encouragement, we may want to put less emphasis on the ultimate causes of the apparent sex differences in achievement. We might instead put our emphasis on efforts toward eradicating these differences, to make sure that all of us—male and female—reach our full potential. Otherwise, as one author put it, we may “waste a most valuable resource: the abilities and efforts of more than half the world’s population” (Shaffer, 2004).