Nichols and Dime: Recalculating Advanced Stats Using Play-by-Play Data

Recently at his web site, Basketball Geek, Ryan Parker used play-by-play data to calculate Dean Oliver’s offensive and defensive ratings. I’ve decided to use Ryan’s approach (and data!) to calculate some of the other advanced statistics out there, many of which were developed by John Hollinger.

Many of these statistics are usually calculated using estimates based on the data available in box scores. However, with the play-by-play data in hand, we can turn these estimates into actual numbers. To calculate the stats, I used the formulas available in the Basketball-Reference glossary. For today, the following numbers will be presented:

  • Rebound Rate: The number of available rebounds a player collected while he was in the game.
  • Offensive Rebound Rate: The number of available offensive rebounds a player collected while he was in the game.
  • Defensive Rebound Rate: The number of available defensive rebounds a player collected while he was in the game.
  • Assist Rate: There are a few ways to calculate this. I defined it as the percentage of field goals a player’s teammates made that he assisted on while he was in the game.
  • Block Percentage: The percentage of opponent field goal attempts blocked by a player while he was in the game.
  • Steal Percentage: The number of opponent possessions that ended with the player stealing the ball while he was in the game.
  • Usage Rate: The percentage of team plays used by a player while he was in the game.

There are a number of different ways to calculate Assist Rate. I calculated my version based on the method used by people such as Ken Pomeroy and Ed Kupfer. Ryan defines his Assist Rate as the “percentage of possessions used that were assists.” There are subtle differences, I believe.

So what’s the difference between my calculations and the usual ones? The following changes:

  • For rebound rates, the number of available rebounds for a player is usually estimated based on the team’s rebounding rates and the player’s minutes. With my method, the actual number of rebound opportunities is determined.
  • For assist rate, the number of field goals made by teammates when a player is on the court is normally estimated based on the player’s minutes and the team’s total field goals. With my method, the actual number of teammate field goals is determined.
  • For block percentage, the number of opposing field goal attempts when a player is on the court is estimated. I use the play-by-play data to get an actual count.
  • For steal percentage and usage rate, player and team possessions are normally estimated, but we can use the play-by-play to count the actual number of possessions.

The numbers for every player are available in the Google Docs spreadsheet below:

http://spreadsheets.google.com/ccc?key=0AvNKNGJ_AHijdEgwV3FrQ25rVTZVbVR4ZEtYcHp5bkE&hl=en

My next step is to calculate PER using these numbers, and I plan to get to that shortly. Much credit again must go to Ryan Parker for inspiring me to do this.

Seth Carstens