Sports economists use the Noll Scully ratio to compare parity across different sports. It's the standard deviation of winning percentage in the league divided by .5 divided by the square root of m, where m is the number of games in a season. so: SD / (.5 / sqrt(m)). The closer that number is to 1, the more competitive the league. I've always wanted to try it out with hbd, but I'm just too lazy to collect the data.