Do Males and Females Have the Same Distribution of IQ Scores?
Jun 28, 2025
Some researchers have suggested that men show statistically greater variation than women, meaning that although the typical man is not more intelligent than the typical woman, there are more men with exceptionally low intelligence and more men with exceptionally high intelligence. Research has largely confirmed this hypothesis (Saini, 2017, p. 65).
Shortly after intelligence tests were developed, psychologists began examining sex differences in intelligence. By the late 1910s, sufficient research existed to foster substantial debate among psychologists regarding whether average differences existed between males and females and their potential magnitude (e.g., Hollingworth, 1919). Given the transformation in educational and career opportunities for women over the past century, periodically reexamining sex differences in cognitive abilities remains worthwhile.
Shortly after intelligence tests were developed, psychologists began examining sex differences in intelligence. By the late 1910s, sufficient research existed to foster substantial debate among psychologists regarding whether average differences existed between males and females and their potential magnitude (e.g., Hollingworth, 1919). Given the transformation in educational and career opportunities for women over the past century, periodically reexamining sex differences in cognitive abilities remains worthwhile.
Average Sex Differences in Mental Abilities
Global IQ. Early large-scale studies on sex differences in overall IQ revealed minimal differences on the 1916 Stanford–Binet. Among 905 children aged 5–14, females demonstrated higher median IQ than males at most ages, except age 10 (identical medians) and age 14 (a 4-point male advantage). At remaining ages, females scored 1–6 points above males (Terman et al., 1915, p. 559). Another early investigation showed a slight male advantage on the Army Alpha administered to 3,693 students at three midwestern high schools, with approximately 2.9 IQ points favoring males (Madsen & Sylvester, 1919).
These studies exemplify early research on sex differences in intelligence: some investigations showed females performing better on average than males, while others demonstrated the reverse (Hollingworth, 1919). Average sex differences were consistently small across studies. Twenty-first-century studies similarly show minimal or zero sex differences, without consistent patterns favoring either sex (e.g., Calvin et al., 2010). Consequently, most psychologists conclude that no differences exist in average intelligence between males and females (Jensen, 1998; Neisser et al., 1996).
Stratum II Abilities. Comparing global IQ scores for men and women doesn't reveal the complete picture of sex differences in mental abilities. From intelligence testing's earliest days, psychologists observed that certain specific tasks and abilities showed average performance advantages for one sex (Burt, 1917; Terman, 1916). A pattern emerged: females typically outperformed males on verbal tasks and processing speed tasks, while males performed better on non-verbal tasks, particularly visual–spatial tasks.
These sex differences on broad Stratum II abilities have continued into the twenty-first century. In contemporary studies, females tend to excel on highly verbal tests (d = .10 to .50), while males perform better on spatial ability tests, with effect sizes from d = .10 to .90 depending on measurement methods. Men also outperform women on mathematics reasoning tests, with effect sizes of d = .05 to .30 (Feingold, 1992; Lakin, 2013).
Variability Differences
| Cutoff | 5% larger male SD | 10% larger male SD | 15% larger male SD |
|---|---|---|---|
| Above 115 or below 85 | 1:1.07 (52% male) | 1:1.14 (53% male) | 1:1.21 (55% male) |
| Above 120 or below 80 | 1:1.12 (53% male) | 1:1.23 (55% male) | 1:1.35 (57% male) |
| Above 125 or below 75 | 1:1.18 (54% male) | 1:1.36 (58% male) | 1:1.54 (61% male) |
| Above 130 or below 70 | 1:1.25 (56% male) | 1:1.52 (60% male) | 1:1.80 (64% male) |
| Above 135 or below 65 | 1:1.34 (57% male) | 1:1.72 (63% male) | 1:2.16 (68% male) |
| Above 140 or below 60 | 1:1.45 (59% male) | 1:2.01 (67% male) | 1:2.67 (73% male) |
| Above 145 or below 85 | 1:1.58 (61% male) | 1:2.37 (70% male) | 1:3.37 (77% male) |
Table 27.1. Female-to-male ratios beyond an IQ cutoff score with no average sex difference
Beyond mean differences, some psychologists have investigated variability in intelligence test scores across sexes. This research tradition dates to intelligence testing's beginnings. Feingold (1992) found that across 28 subtests on 5 intelligence and academic tests, 24 subtests showed greater variability for men than women, with men's standard deviation averaging 5.8% greater per subtest. Subsequent studies produced similar results for global IQ, with most showing that standard deviation for men was 5–15% larger than for females.
This greater male variability has significant implications at the extremes. If both sexes have equal means and males have 5% greater standard deviation, there are 1.07 males for every female above an IQ of 115. As cutoffs become more extreme, the imbalance increases dramatically. At IQ 145, there are 1.58 males for every female.
| Cutoff | 5% larger male SD | 10% larger male SD | 15% larger male SD |
|---|---|---|---|
| Above 115 | 1:1.44 (59% male) | 1:1.52 (60% male) | 1:1.60 (62% male) |
| Above 120 | 1:1.58 (61% male) | 1:1.73 (63% male) | 1:1.86 (65% male) |
| Above 125 | 1:1.76 (64% male) | 1:2.00 (67% male) | 1:2.24 (69% male) |
| Above 130 | 1:1.97 (66% male) | 1:2.35 (70% male) | 1:2.76 (73% male) |
| Above 135 | 1:2.23 (69% male) | 1:2.82 (74% male) | 1:3.48 (78% male) |
| Above 140 | 1:2.57 (72% male) | 1:3.47 (78% male) | 1:4.54 (82% male) |
| Above 145 | 1:2.97 (75% male) | 1:4.33 (81% male) | 1:6.03 (86% male) |
Table 27.2 Female-to-male ratios beyond and IQ cutoff score with a d = .20 mean male advantage
| Cutoff | 5% larger male SD | 10% larger male SD | 15% larger male SD |
|---|---|---|---|
| Above 115 | 1:0.80 (44% male) | 1:0.86 (46% male) | 1:0.92 (48% male) |
| Above 120 | 1:0.79 (44% male) | 1:0.89 (47% male) | 1:0.98 (49% male) |
| Above 125 | 1:0.79 (44% male) | 1:0.92 (48% male) | 1:1.06 (52% male) |
| Above 130 | 1:0.79 (44% male) | 1:0.98 (49% male) | 1:1.18 (54% male) |
| Above 135 | 1:0.80 (45% male) | 1:1.06 (51% male) | 1:1.34 (57% male) |
| Above 140 | 1:0.82 (45% male) | 1:1.16 (54% male) | 1:1.57 (61% male) |
| Above 145 | 1:0.85 (46% male) | 1:1.29 (56% male) | 1:1.88 (65% male) |
Table 27.3 Female-to-male ratios beyond an IQ cutoff score with a d = .20 mean female advantage
Consequences of Score Differences and Conclusion
These differences manifest in real-world selection processes. Males comprise 60.1% of Jeopardy! contestants and win 69.7% of games, make up 62% of special education students, and represent 89.3% of National Geography Bee finalists between 2014-2018.
While males and females possess equal average intelligence, their ability distributions differ in important ways. Males demonstrate 5–15% greater variability, creating higher percentages of males at both high and low extremes of most abilities. The cause remains unclear, though the substantial overlap between groups emphasizes the importance of judging individuals based on personal accomplishments rather than sex.
From Chapter 27 of "In the Know: Debunking 35 Myths About Human Intelligence" by Dr. Russell Warne (2020)
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