Tuesday, January 22, 2013

From "Will they be champs?" to "Will they make the playoffs?"

I have not posted any basketball-related articles since sharing my data-driven predictions for the 2012 NBA Finals (unfortunately for me, the data suggested the Oklahoma City Thunder had a slight advantage against the Miami Heat).

But there has been SO much talk recently on the Los Angeles Lakers' performance that I just had to take a stab at predicting their season outcome.


For those of you not too familiar with the situation, it has all the drama of a Hollywood script, and I will briefly summarize the situation.

The Lakers have had great results in the past years, winning the championship in 2009 and 2010, and being tough opponents in the other years. Over the 2012 summer and a disappointing 2012 year, they signed a couple of superstars: Steve Nash from Phoenix, desperate to win a championship and one of the league's top point guards, as well as Dwight Howard from Orlando, who can be quite a beast under the basket. On paper they were an All-Star team, nobody contested that. Almost everyone had them reaching the Finals, the only question was whether they would beat Miami or not.

But their performance so far surprised even the most pessimistic: they started the season by accumulating losses, and have lost more games than they have won since the start of the season. Things get worse as they are in the Western Conference which is much more competitive than the Eastern conference. Add in a fired coach, a surprising replacement coach, and you have all the drama necessary for a lot of ink to be poured!

Total confusion on the court has been a common sight in the Staples Center:

And so the questio has become: will the Lakers even make it to the NBA playoffs? Only the best eight teams of the Western conference make the playoffs. Many analysts have looked at historical data, noticing that the eight team in the West has an average of 48 wins, and if the Lakers want to reach 48 wins this season they need to start winning fast.

I've decided to take a slightly different approach, by tring to forecast what the rest of the season would look like for all teams based on the first half of the season. Also, the previous methodology ignores what the rest of the teams are doing in your conference, as well as the impact of playing another team also fighting for a playoff spot. When you win against one of those teams, it basically counts double!


Here's the methodology I've taken:
  • extract all of the 2012-2013 season scores and schedule data for all teams, namely home and away winning percentages
  • for all upcoming games I compute the home team's probability of victory as follows:
    home team winning percentage / (home team winning percentage + away team winning percentage).
    For example: Let us say that Chicago with a 12-5 road record (70.8% road winning percentage) is visiting Miami with a 16-3 home record (84.2% home winning percentage), I would estimate Miami's probability of winning the game as:
    84.2% / (84.2% + 70.8%) = 54.4%.
  • Based on this probability, I simulate the game's outcome and then update Chicago's and Miami's records (if Chicago wins, their road record is now 13-5 and Miami's home record becomes 16-4).
  • I continue proceeding that way until all the season's games have been simulated. This then becomes one possible outcome for the season.
  • I then repeat the entire process outlined above thousands of time to get an idea of all the scenarios that can play out.
Based on the simulations, I can then determine which teams are most likely to have the best record in the NBA, and, going back to our original question, how likely the Lakers are to make the playoffs.


Here are the results (based on scores up to 21/01/2013):

Top three NBA records:
  • First place:
    Oklahoma City Thunder (32.9%), San Antonio Spurs (29.2%), Los Angeles Clippers (28%)
  • Second place:
    San Antonio Spurs (26.6%), Oklahoma City Thunder (24%), Los Angeles Clippers (23.4%)
  • Third place:
    San Antonio Spurs (18.7%), Oklahoma City Thunder (17.6%), Los Angeles Clippers (17.1%)
Clearly, the odds are that these three teams will enter the playoffs with the best records and so most likely a Western Conference team will have homecourt advantage in the Finals!

As for the Lakers, here are the probabilities of their final standing in the Western conference:

Position Probability
6 0.4
7 1.4
8 4.1
9 8.9
10 12.6
11 18.1
12 24.2
13 16.9
14 10
15 3.4

Wow! Only a 5.9% probability of the Lakers making the Playoffs!

But let's still monitor them closely, and I'll update these results in the weeks to come.

Please leave a comment if you have any questions/suggestions on the methodology and/or results!



  1. This approach has a problem. The Lakers odds were obviously better than their record because a) any new team with a new coach will be bad, b) any team with numerous injuries will be bad, and c) both of those situations tend* to improve over time. The story is how much resistance there was in regressing upwards to the team's mean, not how they exceeded the odds to make the playoffs.

    *The tendon doesn't change the tendency. It just makes us want to cry along the way.

  2. Thanks for your comment William. Indeed, if a team has a terrible start (new coach, new players, injuries, bad luck), these early results will have a huge impact n predictions throughout the season. I am currently working on an improved approach that will weigh performance and give more weight to recent games than first games of the season. This should allow the model to more accurately estimate the team's true mean.