Mains: The democratization of dingers

From SABR member Rob Mains at Baseball Prospectus on May 11, 2017:

Many baseball fans know that in 1927, Babe Ruth hit 60 home runs. Lou Gehrig hit 47. The Cubs’ Hack Wilson hit 30, as did the Phillies’ Cy Williamson. The Giants’ Rogers Hornsby hit 26, and his teammate Bill Terry had 20. That’s it—nobody else hit 20 or more round-trippers.

In 1927, there were 16 major-league teams. Let’s call the top 16 home run hitters in the majors—one per team—the “elite” sluggers that year. Ruth, Gehrig, Wilson, Williamson, Hornsby, Terry, and 10 guys who hit 14-19 bombs. Those 16 players hit 372 home runs that year. Across the majors, there were 922 home runs. So the elite 16 players accounted for over 40 percent of all home runs that year. Since 1920, the year Ruth hit 54 home runs, 1927 is the only season in which the elite home run hitters—defined as the top n in the majors, where n equals the number of teams—hit over 40 percent of all homers.

Fifteen years earlier, in 1912—two years before Ruth’s first appearance in the majors, not that that’s in any way relevant—the Italian statistician Corrado Gini created a measure, now known as the Gini Coefficient. The Gini Coefficient measures inequality among values in a distribution. It ranges from 0 (perfect equality) to 1 (perfect inequality). Gini proposed it as a measure of income or wealth inequality, and that’s its most common usage, though it can be used to measure the inequality within any dataset.

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Originally published: May 11, 2017. Last Updated: May 11, 2017.