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Blame Math for Women's Inconsistency in Tennis

New research shows that playing five sets per match instead of three would close most of the gap between male and female players.
(Photo: Antoine K/Flickr)

(Photo: Antoine K/Flickr)

Women's tennis is an inconsistent game compared to the men's version, full of ups, downs, and short-lived phenoms. That's been attributed to biology, the conflict between work and family, and even excessive deference to overbearing coaches. But really, it's a matter of probability and statistics, according to research presented over the weekend at the Joint Statistical Meetings in Seattle.

In one sense, women are more inconsistent than men in professional tennis, argues Stephanie Kovalchik, an associate statistician at the RAND Corporation. Upsets are more common than in men's tennis, as are letdowns, where a player wins big in one match and then tanks in the next. High-ranked men are also more likely to win their matches than equally ranked women. Curiously, however, those differences only show up in Grand Slam tournaments—Wimbledon and the United States, Australian, and French Opens—and not in less-prestigious tournaments.

Of course, there's no shortage of people chiming in with the usual sex-based explanations and assumptions. A 2012 analysis in the Economist suggested that rules allowing women to turn pro "before their bodies had acquired the necessary resilience" could well be to blame, as might family conflicts and coaching dynamics. Others seem to take sex-based differences for granted.

The more sets she plays per match, the more consistent she'll appear.

But Kovalchik noticed another difference between men and women (as had someone who commented on the Economist story, incidentally): In Grand Slam tournaments, women play best-of-three matches; men play best-of-five.

From a probability and statistics point of view, that's important. Think of a tennis match as a way of determining the better player. But it's an imperfect process—one in which the truly better player wins only some of the time. For example, imagine the better player wins 60 of her matches. That means there's only a 60 percent chance a single match will correctly identify the better player.

Now, with odds like that, no sane official (or bookie) would rely on just one set to determine who the better player is. Instead, players compete in multiple sets, and the more, the better. Crunch the numbers and you'll learn that a player who wins 60 percent of her individual sets will win, on average, 64 percent of her best-of-three matches and 68 percent of her best-of-five matches. In other words, the more sets she plays per match, the more consistent she'll appear.

Kovalchik took this argument one step further and calculated what advantage higher-ranked women and men would have if they played three versus five sets in a match, based on 2010–2014 Women's Tennis Association and (men's) Association of Tennis Professionals win-loss percentages. While the men were a little bit more consistent—that is, men won slightly more of their matches compared to equally ranked women—the gender gap was small compared to the difference created by playing three versus five sets per match.

All of which is to say, do the math before saying boys are better at sports.

Quick Studies is an award-winning series that sheds light on new research and discoveries that change the way we look at the world.