Luigi Guiso, Ferdinando Monte, Paola Sapienza, Luigi Zingales:

results, we classified countries according to several measures of gender equality. (i) The World Economic Forum’s Gender Gap Index (GGI) (10) reflects economic and political
The existence (1), degree (2), and origin (3, 4) of a gender gap (difference between girls’ and boys’ scores) in mathematics are highly debated. Biologically based explanations for the gap rely on evi- dence that men perform better in spatial tests, whereas women do better in verbal recall ones (1, 5, 6). However, the perform- ance differences are small, and their link with math test per- formance is tenuous (7). By contrast, social conditioning and gender-biased environ- ments can have very large ef- fects on test performance (8).
To assess the relative
importance of biological and
cultural explanations, we
studied gender differences
in test performance across
countries (9). Cultural inequal-
ities range widely across
countries (10), whereas re-
sults from cognitive tests do
not (6). We used data from
the 2003 Programme for
International Student Assess-
ment (PISA) that reports on
276,165 15-year-old students
from 40 countries who took
identical tests in mathematics
and reading (11, 12). The
tests were designed by the Organisation for Economic Co-operation and Develop-
ment (OECD) to be free of
cultural biases. They are sufficiently chal- lenging that only 0.6% of the U.S. students tested perform at the 99th percentile of the world distribution.

by country (see chart, above): in Turkey, –22.6, whereas, in Iceland, 14.5. A similar variation exists in the proportion of girls over boys who score above 95%, or 99% of the country-level distribution (fig. S2A).
opportunities,
Math and reading gender gaps. In more gender-equal cultures, the math gender gap dis- appears and the reading gender gap becomes larger. (Top) Gender gaps in mathematics (yellow) and reading (gray) are calculated as the difference between the average girls’ score and the average boys’ score. A subset of countries is shown here (see SOM for complete data set and calculations). In many countries, on average, girls perform more poorly than boys in mathematics. In all countries, girls perform better than boys in reading. The gender gap in mathematics and reading correlates with country measures of gender status within the cul- ture, one of which measures is the GGI (bottom). Larger values of GGI point to a better aver- age position of women in society. Besides USA, the countries are abbreviated as their first three letters, except for PRT, Portugal, and ISL, Iceland.
The gender gap is reversed in reading. On average, girls have reading scores that are 32.7 higher than those of boys (6.6% higher than the mean average score for boys), in Turkey, 25.1 higher and in Iceland, 61.0 higher (see chart). The effect is even stronger in the right tail of the distribution. In spite of the difference in levels, the gender gap in reading exhibits a variation across countries similar to the gender gap in math. Where girls enjoy the strongest advantage in reading with respect to boys, they exhibit the smallest disadvantage (sometime even an advantage) in math. [The correlation between the average gender gaps in mathematics and reading across countries is 0.59 (fig. S4)].
0.81), our statistical model suggests that the mean score performance in mathematics of girls relative to boys would increase by 23 points, which would eliminate the Turkish gender gap in math (see table, p. 1165). In more gender-equal countries, such as Norway and Sweden, the math gender gap disappears. Similar results are obtained when we use the other indicators of women’s roles in society. These results are true not only at the mean level, but also in the tail of the distribution (table S3). In Iceland, the ratio of girls to boys who score above the 99th percentile of the country distribution in math scores is 1.17.
70 60 50 40 30 20 10
0 -10 -20 -30
0.8 0.75 0.7 0.65 0.6 0.55 0.5
TUR
Gender gap, math Gender gap, reading
KOR ITA USA PRT
Women’s emancipation (GGI)
FRA POL
NOR SWE ISL
GGI index Test score differences between girls and boys