Tuesday, August 17, 2004
lady luck
Ken Pomeroy is up with a few great posts on the luckiest and unluckiest clubs of 2004.How does the stat man quantify luck?
Using an adaptation to Pythagorean Theorem of Baseball. Conceived in the 1980s by statistician Bill James, the "theorem" predicts the winning percentage of a baseball team based on how many runs the team scores and how many runs it allows.
Expected Winning Percentage = RunsScored^2 / (RunsScored^2 + RunsAllowed^2)
If a team's actual winning percentage is lower than it's expected percentage, it is a beneficiary of good luck. If the opposite is true, it is a victim of bad luck. Further, as Ken notes:
If a team wins a lot of close games and loses a few blowouts, their actual record would exceed their "Pythagorean record." They would be the beneficiary of luck, because you would not expect them to be dominant in close games especially given that they had a few lopsided losses. The opposite case would indicate a team is unlucky.
To apply James' formula to basketball, Ken raised points scored and points allowed to the 10th power.
Expected Winning Percentage = PointsScored^10 / (PointsScored^10 + PointsAllowed^10).
His results?
Louisville (3.8 less wins than expected), Arizona (2.6), Cal Santa Barbara (1.9), Pennsylvania (1.9), and Florida State (1.8) were among the unluckiest teams last season. Look for each to improve this year.
Southern Illinois (3.0 more wins than expected), Wisconsin Green Bay (2.7), Stanford (2.1), Syracuse (2.1), Princeton (2.0), Tennessee (1.9), and Virginia (1.8) were the luckiest teams this season. Look for each to regress this year.
