Here is my most recent FanGraphs piece. (It made The Best of FanGraphs list for last week!) It revisits the work I did in September on parity between the two leagues. At the time, I noted that the American League, perceived as being weak this year, in fact is overall better than the National League (as measured by interleague won-lost record). I attributed the perception of weakness to the near-record level of parity in the American League, with neither notably strong nor weak years. As measured by the standard deviation of wins, in fact, the American League in 2015 had, at the time, the highest level of parity in the 30-team (since 1998) era.
With the regular season in the books, there are two conclusions. First, parity in the American League didn't turn out to be the highest of the 30-team era. It was the highest of all time. Here is a list of the standard deviation of wins, i.e., the "plus or minus x" amount in the phrase, "The average team had 81 wins, plus or minus x." Here's a list of the ten seasons with the lowest standard deviation of wins since 1901:
The American League this season was the most equal league in major league history.
Despite that parity, the American League clearly was the superior league, for the twelfth straight season:
As with every season, there have been storylines that are unique to the 2015 baseball season. The remarkable infusion of young talent to the game. The relevance of the Cubs and Astros after years of being doormats. The disarray in Boston and Detroit. And, of interest here, the general ineptitude of the American League.
I analyze this supposed AL inferiority in this article on FanGraphs, and this one in Banished to the Pen. The FanGraphs article has data through games of September 5, while the Banished to the Pen piece is through September 9. The conclusion of each is the same:
The record level of parity in the American League to date has smoothed out the top and bottom of the league, resulting in hardly any notably bad or notably good teams. But that parity shouldn’t be mistaken for weakness. The American League is the better league overall, as evidenced by its clearly superior record in interleague play. The National League may have the best teams, but the American League remains the better league.
