Birthday as (Athletic) Destiny

Growing up in Boston, my goal was to play first base for the Red Sox. After a mediocre high school and college career, I hung up the spikes for good. It turns out the my failing owed more to my July 27 birthday than to my inability to hit a curveball: The Boys of Late Summer: Why Do So Many Pro Baseball Players have August birthdays? (Slate), by Greg Spira:

Since 1950, a baby born in the United States in August has had a 50% to 60% better chance of making the big leagues than a baby born in July. The lesson: If you want your child to be a professional baseball player, you should start planning early. Very early. As in before conception.

The table below lays out the full month-to-month data. ...

The pattern is unmistakable. From August through the following July, there is a steady decline in the likelihood that a child born in the United States will become a major leaguer. Meanwhile, among players born outside the 50 states, there are some hints of a pattern but nothing significant enough to reach any conclusions. ...

The magical date of Aug. 1 gives a strong hint as to the explanation for this phenomenon. For more than 55 years, July 31 has been the age-cutoff date used by virtually all nonschool-affiliated baseball leagues in the United States. ... (There is no such commonly used cutoff date in Latin America.) The result: In almost every American youth league, the oldest players are the ones born in August, and the youngest are those with July birthdays.

The authors of Freakanomics chronicled a similar birthday effect with January-March birthdays in European soccer. Unfortunately, I did not learn of this birthday effect in time to help my kids, who have both managed to become quite good high school athletes despite having non-advantageous May and June birthdays.

Note to Bill Henderson and the Empirical Legal Studies team: what is the optimum birthday for a law professor?

Cross-posted on TaxProf Blog.