If there’s one group of people who are as obsessed as we are with rigorously analyzing a complicated domain and figuring out where to prioritize scarce resources, it’s Major League Baseball front offices. With that in mind, we wanted to write this guide comparing some baseball statistics with the metrics we take into consideration when evaluating programs to save and improve lives.

Batting Average: Batting average is simple to calculate and easy to explain, and it was historically considered one of the most important ways of evaluating how good a player was. It remains one of the primary baseball stats you’ll find in the newspaper.

But as a measure of a player’s value, batting average isn’t actually all that helpful—and at times can be actively misleading. One of the two primary shortcomings of batting average is that it ignores plate appearances that end in a walk. But walks are really valuable! The Little League wisdom that “a walk is as good as a hit” is an oversimplification, but it also points us toward a statistic that’s more valuable than batting average. It turns out that on-base percentage, which considers walks (as well as the less common hit-by-pitch method of reaching base) as a successful outcome, is a better predictor of a player’s offensive value.

As an example, Juan Pierre and Adam Dunn, who both played in about 2,000 games over their careers, had lifetime batting averages of .295 and .237 respectively. At first glance this might give the impression that Pierre was the more productive hitter. Looking at on-base percentage though, we see that Dunn actually reached base more frequently than Pierre (.364 versus .343), which, combined with his propensity for hitting home runs (another indicator of offensive value that batting average ignores), made him the much more valuable career hitter. (Dunn’s negative defensive contributions are another story.)

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