NBA Playoff Win Probabilities

Live win probabilities for NBA playoff games are available at Previous final games are here. The WP graphs include new features and stats. Some of the recent additions include:

Possession Value (PV): The value in WP of simply having the ball. Defined as the ‘next expected’ outcome of a possession, usually 20 sec off the clock, 10% chance of a 3-point gain, 35% chance of a 2-point gain, and a 10% of a 1-point gain.

Leverage Index (LI): A ratio of the current Poss Val to the an NBA game’s typical possession value, which is 0.04. So when the Poss Val might be 0.10 toward the end of a close game, the LI is 2.5.

Comeback Factor (CF): A measure of how big a comeback the game comprises. Based on the current winning team’s lowest WP at any point in the game. Adjusted to a scale of 1-100. Technically defined as 1/(lowest WP). For example, a team that has come back from a 0.10 WP to lead or win a game has a CF of 1/0.10 = 10. An epic comeback from a 0.01 WP would be 1/0.01 = 100.

Excitement Index (EI): (I need a better name for this.) Based on the net average deviation of the game’s WP from 0.50. A blow-out where one team takes the WP to 0.99 or 0.01 for most of the game will have a large deviation (boring). A game that teeters around 0.50 WP will have a small deviation (exciting). A game where the advantage swings wildly back and forth between teams (also exciting) will also have a small net deviation of 0.50 because the large swings cancel out.

One of the reasons I'm tinkering with the NBA win probability now is as a dress rehearsal for the upcoming NFL season. I'm working on analogous features and stats for NFL games. By the start of the NFL season I should have a pretty comprehensive WP site. Toward the end of last season, there was a healthy discussion on how to measure the 'excitement' value of a game. I think I've got a good foothold now on how to do that.

Here's a sample of what the NBA graph looks like right now. This is from a final game, a live game will have some added stuff.

If anyone is interested in the inner workings of the basketball WP model, you can check my post at the Wages of Wins blog. As always, comments and suggestions are appreciated.

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3 Responses to “NBA Playoff Win Probabilities”

  1. Sky says:

    Just finding this, and think it's awesome. Have you thought about defining something like the EI as the sum of the absolute values of all the changes in win probability? Near a win expectancy of 50%, lots of changes will really add up. At the extremes, the changes are small, and won't be that large.

  2. Brian Burke says:

    Sky-thanks. Great idea. Yup, that's exactly what I'm going to do. Someone had actually suggested that back in my post on the Super Bowl. Right now the "EI" is pretty worthless.

  3. Ty Willihnganz says:

    Brian, thanks for your work throughout the NBA playoffs. I tried to hype your charts as much as I could.

    Do you think there is a way to apply your leverage index and your formulas to devise something like a pro basketball version of the "Player Win Average" statistic the Mills Brothers created for baseball back in the 70s or whenever? That would be interesting.

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