By David RoherA league is considered to have parity if there is not a wide difference in talent level between the best and worst teams. An easy way to measure that is to find the standard deviation of win totals among the teams in the league for any given year. Thanks to the amazing Baseball Reference, I was able to compile the standard deviation for every year from 1901 on. Basically, the way to interpret the graph is that the smaller the standard deviation, the greater the parity in that year. There’s a lot of interesting stuff to find in this graph, and I hope that some of you will point them out in the comments. Here are some of my thoughts:
– There is a clear upward trend in parity (downward trend in SD) over the course of MLB history. It was lowest in the earliest parts of the dead ball era, but increased throughout the dead ball era and into the first part of the 1920s. After a level period of about 20 years, there was a steep upward parity trend until the 1980s. From that point on, parity decreased until the turn of the 21st century. We currently appear to be on another parity increase swing (though not as steep as the best fit curve would indicate).
– My best guess for the cause of this increase is the increase in talent level. There’s no question that players today are stronger and more talented than their earlier counterparts. This isn’t to diminish those who succeeded before the current era at all – they didn’t get the same benefits of improvements to equipment, training and, uh, nutrition that today’s guys do. But when everyone gets more talented on average, the playing field gets leveled. Think about college sports compared to professional leagues – in college, a strong or weak strength of schedule can make or break your season, while that is only true to a much lesser extent in the pros.
– It’s interesting that parity stopped its mid-century increase right around the time of the beginning of the free-agent era. However, it is unclear what effect that has had. Also worth noting is that the decrease in parity stopped right around 2001, and that revenue sharing was implemented one year later. But there’s not enough evidence here to see if those two things are related.
What do people think? I would hesitate to look at specific years, as I think a lot of that is noise. But I think the trends might be interesting. Additionally, how else can we measure parity?