Thursday, August 6, 2020

WSJ: What the Numbers Say About Gender Differences

 


Data on abilities reveal a great deal of overlap for men and women

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In 2005 Lawrence Summers, then the president of Harvard, caused an uproar by appearing to suggest that the lack of women professors in math and science might arise from biological differences. Fifteen years on, a gender imbalance in these fields persists and the arguments rage on. I believe math can help us to progress.

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The discipline of math involves, among other things, ironing out ambiguities and providing clear definitions for comparisons. Men and women are not homogenous groups of people who all behave in the same way, so we need ways to understand whole sets of data. 

Averages are one well-known way; we can compare how men and women do at something “on average.” There are different types of averages: The mean is where we add up all results and divide by the total number of people, and the median is the 50th percentile that tells us that half the people rank above it and half rank below. For example, the mean height of men in the U.S. is 5 feet 9 inches, and for women it is 5 inches less, but plenty of women are taller than plenty of men. Averages don’t tell us much about differences among entire sets of data because they neglect how widely the data are spread.

That spread of data can be studied via the standard deviation, which is calculated from the distance that each data point ranges from the mean. For a standard bell curve, a distance of “one standard deviation” on either side of the mean always comprises a fixed proportion of the results, around 70%. 

Average marathon times for men and women differ by about 30 minutes. That sounds like a lot, but the fastest women run marathons twice as fast as the average men.

The standard deviation for height is around 2.5 inches, so the mean heights of men and women are about two standard deviations apart. Thus, around 95% of women are shorter than the average for men, but there is still a noticeable overlap. For data sets that differ by one standard deviation or less, there is more substantial overlap. 

Average marathon times for men and women differ by about 30 minutes, for instance. That sounds like a lot, but is only half the standard deviation of one hour—and the fastest women run marathons twice as fast as average men.

Height and running times are particularly easy to measure, but men and women have also been compared in broader areas of behavior, such as mathematical skills, aggression and self-esteem. 

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In 2005, Jane Shibley Hyde collated a large collection of meta-analyses of these differences. In her book “Inferior,” Angela Saini sums up the results: “In every case, except for throwing distance and vertical jumping, females are less than one standard deviation apart from males. On many measures, they are less than a tenth of a standard deviation apart, which is indistinguishable in everyday life.” For example, “mathematics problem solving” was found to be better in men by just 0.08 standard deviations; interestingly, women were found to out-perform men at “mathematics concepts” by 0.03 standard deviations. Men showed more self-esteem by a range of 0.04 to 0.21 standard deviations, increasing through adolescence; they were found more likely to make “intrusive interruptions” by 0.33 standard deviations.

The differences may be interesting, but they are also very small. The differences within each gender are greater than the differences between genders, so gender is not a good predictor of these behaviors.

Such comparisons are blurred, of course, by issues beyond the reach of mathematics. Many of the behaviors studied are much harder to define and measure than height or marathon times and involve some mix of biological and sociological influences. But it is logically flawed to infer a biological difference from a statistical difference. Mathematics provides us with powerful tools, but we have to know their uses and limits. 

—Dr. Cheng’s new book, “X+Y: A Mathematician’s Manifesto for Rethinking Gender,” will be published Aug. 25 by Basic Books.

https://www.wsj.com/articles/what-the-numbers-say-about-gender-differences-11596752225


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