Archive for the 'Projections' Category

They've been having a spirited debate about retrodiction over at APBRmetrics recently, and apparently we're all going to engage in some sort of challenge over whose pet metric could "retrodict" a team's 2009 performance the best. This, of course, should be nothing new to faithful readers of the BBR blog, because we retrodicted 2008-09 several months ago. But my question is, does accurate retrodiction across the entire league really "prove" anything? For the vast majority of teams, any cheeky wee monkey is going to be able to predict performance effectively based on data from the past few years because A) roster turnover is rarely drastic enough to the point that a team's stars are no longer with the team anymore, and B) even in the case of roster shakeups, coaches almost always employ new players in the same role they had been playing in for their previous team. Since we know a lot of basketball productivity is role-specific, there's really not a lot of point in boasting that past production in your metric predicted future production when a player plays exactly the same role in each situation.

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In the final installment of the season, here's your official Statistical +/- prediction for the 2009 Finals:

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Using the technique I introduced a few weeks ago, here's what Statistical +/- sees in the cards for the Conference Finals:

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A week ago, we delved deeper into our new Statistical Plus/Minus results and tried to retrodict the standings for the regular season, coming within a healthy +/- 6.6 wins per team. Now the question is, can we put the same method to the test for a playoff series? Let's use the recently-completed first round as a test case...

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Last week, I promised that we'd see how well our new statistical +/- formula "retrodicted" this season, and today seems like a good time to follow through on that.

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Surely most of our readers have heard about "adjusted plus/minus" at some time or another, whether through TrueHoop, Sports Illustrated, the APBRmetrics board, the many articles at 82games on the subject, or even Michael Lewis' article about Shane Battier in last week's New York Times Magazine. But for those of you who aren't familiar with the stat, it essentially tracks a player's influence on his team's point differential by comparing the team's performance when he's on the court vs. its performance with him sitting on the bench. There are also adjustments for a player's teammates, backups, opponents, and even the location of each game, and the whole mountain of data is fed through a massive linear regression equation to try and isolate the individual impact of every player. Personally, I believe this system has a lot of promise (especially with regard to measuring defense), and with further refinement it will one day be one of the better basketball metrics out there, so it was nice to see it get some more recognition this past week -- even though there are still some wrinkles that need to be ironed out.

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Back in October, Basketball Prospectus' Kevin Pelton introduced the SCHOENE projection system. Kevin's system is quite detailed, so rather than summarize it here I would encourage you to read his article. Around the same time Kevin released SCHOENE, I came up with the Simple Projection System, or SPS. The SPS is very simple (hence the name), and is described in full in the previous link. Since we are nearing the midpoint of the 2008-09 season, I thought it would be interesting to see how these two new projection systems are faring.

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