IStock Photo 1707480 © RBFried

In developing the Book of Odds, our researchers meet weekly to review their work with each other. We often have visitors. On this day our visitor was a college student, the daughter of a close friend. The presentations she saw were really varied: one researcher had just completed work on the odds associated with contraception, another one had compiled the odds on baseball.

The odds of a woman becoming pregnant after relying on one form or other of contraception were displayed. Starting with the population of women in 2002 who were of child-bearing years (15 - 44), the presentation identified the odds that one of these women was sexually active, the odds that she relied on condoms for contraception, and the odds that she would stop relying on condoms because she was pregnant. Each step of this “thread” of probabilities (as we term such chains) had independent odds. When put together, the odds that a woman in that original group would end up having given up condoms because there was no longer any point—she had become pregnant despite the contraceptive measure—were 1 in 142.

Next came the baseball presentation, and as it happened, our visitor was a baseball fan. She seemed captivated as the Book of Odds baseball statistics were summarized. They were different from those she was used to on the sports pages. Instead of abstract measures such as Earned Run Average (ERA), something no one literally can see, or sophisticated inventions such as Bill James’ “Runs Created,” the perspective taken was that of a fan at the ballpark at the moment the pitcher is poised on the rubber. What will happen next on average, independent of who’s pitching and who’s batting? Viewed this way, the odds that the next batter will hit a triple are 1 in 144.

Later that day I received a call from my friend, the college student’s mother. Her daughter had returned home on a mission. She had immediately called her boyfriend, and her mother overheard her daughter’s part of the conversation. “She asked her boyfriend if he knew the odds of a couple conceiving a child if they were relying solely on condoms,” my friend said. “She informed him that the odds were 1 in 142.

“Then she asked if he knew the odds of the next batter in a Major League game hitting a triple. Again, he didn’t seem to know.

“‘It’s 1 in 144,’ she told him. And then she added emphatically, ‘And you know what? I’ve seen triples.’”