Competitive Balance Throughout NBA History

In my previous post, I asked whether competitive balance in the NBA had decreased in recent years, after determining that this year's group of teams that trailed 2-3 in a 7-game series (after being tied 2-2) were actually less evenly matched than the historical series comeback rate of 18% indicated.

To compare season-to-season competitive balance, I used the Noll-Scully Measure (NSM), which is the ratio of the actual standard deviation in each to season to the "ideal" standard deviation for that season. The lower the NSM, the greater competitive balance (CB) there is in the league. A perfectly balanced league would have a ratio of 1; if the ratio is less than 1, than the teams are even closer in wins than we would expect (which does happen, although rarely).

The NBA was formally created in 1950, and there have been many changes to its playoff structure (remember the original purpose of this research looked into 7-game series), but at least one round of the playoffs has always been a 7-game series. Thus, I calculated the NSM for each season for the entire history of the NBA since 1950:

There's a good deal of variation in the league's competitive balance, but there doesn't appear to be a significant trend to indicate less balance recently (although the ratio did drop below 1 for a brief period of time way back in the 1950's). Even so, this year's NSM is 2.92, which is above the average of 2.58 (and thus indicates below average CB for this season). In fact, the NSM has been above this average in 7 of the last 8 seasons:

Year	NSM
2015	2.922779391
2014	2.805581752
2013	2.763560925
2012	2.494208925
2011	2.86081387
2010	2.901691628
2009	3.064976463
2008	3.004894569

This isn't definitive, but maybe CB actually has decreased in recent seasons.