By: Edward Egros

Playoffs

Playoff Unpredictability

Pasted GraphicUntil recently, the Los Angeles Lakers were one of the fixtures of the NBA Playoffs, and in many seasons, the Finals. They have put together dynasties in different generations of the sport, from Magic Johnson's teams to the Shaq and Kobe era. When the Lakers were not winning titles, chances are another team was enjoying its own dynasty, like the Boston Celtics, Chicago Bulls or San Antonio Spurs. Dynasties are so commonplace in the NBA, 15 franchises in the sport's history do not have a championship (and seven of those still in existence never even made it to the Finals).

The NBA is unique in this regard: championships are won in bulk. Other leagues offer more parity, where there is a larger pool of contenders vying for a title. There may be dynasties in other sports, but there seems to be fewer of them, each shorter in duration and there stood a better chance someone unexpected can claim the sport's top prize.

Which of the four top professional sports leagues (NFL, NBA, MLB and NHL) offers the most playoff unpredictability? Is the NBA truly the most predictable? Is it significantly more predictable or marginally so?

One approach to answering these questions is by using a statistical model for each sport. Here, we will use
logistic regressions, where we will look at only wins (or points in hockey) and see how well it predicts whether a team won a championship that year. Here are some other notes for setting up this project:

- All data used begins with the 1989-90 season because
the NFL had the biggest chance to its playoff format at the turn of the new decade.

- Any season in any sport where a lockout shortened the number of games played considerably was removed (e.g., the 1998-99 NBA season, the 2012-13 NHL season, etc.)

- Though the NHL played 80 and 84 games in a few of these seasons, these numbers are not significantly different from the 82 played the rest of the dataset, so they are still used.

At first glance, every variable representing wins is statistically significant with 99% confidence, which should be obvious because you need so many wins just to make the playoffs. What matters is how well wins alone predicts championships. In statistical parlance, we will use a goodness-of-fit measure called
AIC (Akaike Information Criterion) to answer this question. As this number gets smaller, the model has a better fit. The following shows how well each model performs:

Screen Shot 2016-04-17 at 7.47.11 AM
The larger the bar, the more unpredictable the league is. Again, as expected, the NBA is the most predictable, and by a considerable margin. This model also suggests Major League Baseball is the most unpredictable, with the NFL as a close second and the NHL as a close third.

There are a number of other variables that could be added to these models to help determine who will win a championship, but the simplicity of these models makes for an easier comparison across sports.