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Evan Horowitz

In baseball, 30 is over the hill

Age matters in baseball. Players tend to get better through their twenties, and then to decline through their thirties. This doesn’t mean teams should just dump players on their 30th birthday. In fact, age is much less important than talent, and a great player at 35 is often vastly better than a mediocre player at 25.

But age is certainly something to consider when rebuilding a team or signing long-term contracts.

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It is one of the things the Red Sox have been considering this week. As the trade deadline approached, they faced a choice between restocking for next year with promising young players or hold out and hope for veterans to return to World Series form. The last few frantic days of trading suggest they’re not betting on veterans. They gave up five players with an average age of 32, and got five new players with an average age of 27. Statistically speaking, that may be a good deal.

When do players peak?

There are various ways to estimate peak performance, but one of the most thorough comes from an economist named J.C. Bradbury. He looked at 80 years of baseball history and found that in general players peak around age 29. Hitters and pitchers alike.

Hitting. The actual peak varies a bit, depending on exactly what skill you’re measuring. Older players have an advantage when it comes to being patient and drawing walks, but batting average and slugging percentage peak earlier, around 28

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Pitching. Like older hitters, older pitchers seem to have a better feel for the strike zone. It’s the 24-year-olds, however, who know how to strike people out.

How important is age, really?

If you were at a fantasy league draft, and the only thing you knew about the players were their ages, the best strategy would be to pick 29-year-olds. That’s the year when baseball players seem to be at their best. In the real world, we know a lot more about players than that. Talent and past performance turn out to be far better predictors than age.

Still, if you’re trying to judge whether it was wise to trade Lester (30) and Gomes (33) for Yoenis Cespedes (28), age is part of that calculation. It’s especially relevent if the only way to keep Lester was to sign him to an expensive, long-term contract that would have him pitching for the Sox through his 35th birthday.

Whenever you’re considering signing veteran players to long-term contracts, you need to think carefully about the impact age will have on future performance. This week, the Red Sox went a different direction and made their team a little younger.

Source: These charts were originally published in J.C. Bradbury’s “Peak athletic performance and ageing: Evidence from baseball

Evan Horowitz digs through data to find information that illuminates the policy issues facing Massachusetts and the U.S. He can be reached at evan.horowitz@globe.com. Follow him on Twitter @GlobeHorowitz
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