Random Chance in Sports

This post is a followup to Random Chance in the NFL which highlighted the lowered competition in the NFL this year. It showed that the best teams win 62% of the time this year, far less than previous years. How often the better team won in previous years and in other sports were still left unknown though. Until now. Here, using the same methodology focusing on variance, here are the data on the last three full seasons in the four major american sports:

	2008	2009	2010
MLB	0.59	0.6	0.59
NBA	0.77	0.77	0.75
NHL	0.56	0.61	0.61
NFL	0.8	0.8	0.78

On average the better team wins 60% of the time in MLB, 77% in the NBA, 60% in the NHL, and 79% in the NFL. But how about this year? How often does the best team win in the NFL this year? It's gotten better since the last look, so far this year in the NFL the better team wins 70% of the time. While this is still an unprecedented increase in parity, it is also slowly getting closer to the norm we'd expect, thanks largely to big losers like the Bills and Panthers. So while this NFL season may have some crazy outcomes, it's still less random than sports like Hockey.

This article originally ran with a bug in the program used to calculate variance. While the effect on previous season results was minimal, it messed with the current season results a lot. The NFL is not actually just random chance this year, although going with just home field advantage would still be pretty good.