Mains: The 2019 season in inequality

From SABR member Rob Mains at Baseball Prospectus on October 9, 2019:

In 2017, I introduced the Gini Coefficient. Well, I introduced it to some of you; others were already familiar with it. The Gini Coefficient, invented by Italian statistician Corrado Gini, measures inequality over a distribution. Gini created the measure to gauge inequality of income or wealth. The Gini Coefficient ranges from 0 (perfect equality) to 1 (perfect inequality). Here’s a standard application, from the Organization for Economic Cooperation and Development, a club of 36 mostly wealthy countries. It shows the Gini Coefficient of disposable income, i.e., income inequality.


As you can see in the chart, the Slovak Republic, Slovenia, and the Czech Republic were the most egalitarian OECD countries in 2018. South Africa, Costa Rica, and Chile were the least. The U.S. was the sixth-most unequal.

In the article to which I linked above, I used the Gini Coefficient to measure inequality among major league players hitting home runs and stealing bases. I’m going to guess that this is not what Gini had in mind when he came up with his metric in 1912. But hey, it worked, even if the application was a bit of a stretch.

Here’s an application that’s less of a stretch: Won-lost records. Yes, they’re not the same as wealth or income. But we can compare teams’ winning percentages in a given season on an equal footing, since they all play more or less the same number of games, easier than we can compare home run totals for a player with 700 plate appearances and one with 70.

Read the full article here:

Originally published: October 9, 2019. Last Updated: October 9, 2019.