Posts Tagged ‘Relative Winning Percentage’

NBA Power Ranking (by Relative Winning %)

January 20, 2010

I have completed another of my objective NBA Power Rankings using the “Relative Winning Percentage” formula.

RWP compares each NBA team’s pythagorean* winning percentage at home and its pythagorean winning percentage on the road to the rest of the NBA’s pythagorean winning percentage against the same home schedule and the rest of the NBA’s pythagorean winning percentage against the same road schedule.  Each team is then ranked according to the average of the two comparisons plus .500%.  That is what I call its “Relative Winning Percentage”.

Sidebar on what the term “Pythagroean” means as used in RWP (explained by basketball-reference.com):

W Pyth
Pythagorean Wins; the formula is G * (Tm PTS14 / (Tm PTS14 + Opp PTS14)). The formula was obtained by fitting a logistic regression model with log(Tm PTS / Opp PTS) as the explanatory variable. Using this formula for all BAA, NBA, and ABA seasons, the root mean-square error (rmse) is 3.14 wins. Using an exponent of 16.5 (a common choice), the rmse is 3.48 wins.  Why do I use this instead of just using straight winning percentage?  I want to eliminate luck to the greatest extent possible.  I’m trying to measure relative strength, not fortuity.

RWP Example:

Using Pythagorean numbers, NBA home teams beat Team X’s home opponents .673% of the time, whereas Team X beats them .796% of the time.  NBA road teams beat Team X’s road opponents .348% of the time, whereas Team X beats them .262% of the time.  Then Team X’s Relative Winning Percentage would be .518%.  Calculation: (.123 – .086)/2 + .500).

RWP is meant to be a simple and reliable method of judging the objective  strength of each team regardless of opponent or location.  It splits each team’s home and away calculations and weights them evenly to favor teams with more balanced strength.

The Movers this week

This week’s RWP Power Rankings are remarkably consistent with the rankings I did on January4th.  Cleveland maintains the NBA’s highest RWP, with Boston supplanting Atlanta in the number two spot.  The largest rise belongs  to the Utah Jazz, which moved up five spots to number 8.  The Sacramento Kings (18 to 22) and the Dallas Mavericks (8 to 12) tied for the largest drop.

One other note.  When you consider the fact that somewhere around 29% of all games (about 24 games) are decided by luck rather than strength, and that a team ought to win half of those games, then the New Jersey Nets could be one of the worst teams in history.  Its RWP of .126% would translate into 10 wins, less than the amount of wins a team should be able to fall ass backwards into (12).  That’s monumentally bad.

Here are the results.  I listed each team’s previous ranking in parenthesis.

NBA POWER RANKING (by Relative Winning %)

1. Cleveland Cavaliers (1)____________________(.678%)

2. Boston Celtics (3)________________________(.676%)

3. Atlanta Hawks (2)_______________________(.666%)

4. Los Angeles Lakers (4)____________________(.657%)

5. Orlando Magic (5)_______________________(.653%)

6. San Antonio Spurs (6)____________________(.639%)

7. Denver Nuggets (7)______________________(.626%)

8. Utah Jazz (13)___________________________(.599%)

9. Oklahoma City Thunder (10)________________(.597%)

10.  Portland Trailblazers (12)_________________(.590%)

11. Phoenix Suns (9)________________________(.586%)

12. Dallas Mavericks (8)______________________(.572%)

13. Houston Rockets (11)_____________________(.537%)

14. Miami Heat (14)_________________________(.521%)

15. Charlotte Bobcats (16)____________________(.510%)

16. Memphis Grizzlies (15)____________________(.504%)

17. Toronto Raptors (17)_____________________(.492%)

18. Milwaukee Bucks (19)___________________(.462%)

19. New Orleans Hornets (20)__________________(.441%)

20. New York Knicks (21)_____________________(.437%)

21. Los Angeles Clippers (22)__________________(.410%)

22. Sacramento Kings (18)____________________(.406%)

23. Chicago Bulls (27)_______________________(.405%)

24. Philadelphia 76ers (26)___________________(.403%)

25. Washington Wizards (25)_ ________________(.383%)

26. Detroit Pistons (23)_____________________(.373%)

27. Golden State Warriors (24)_______________(.368%)

28. Indiana Pacers (28)_____________________(.332%)

29. Minnesota Timberwolves (29)_____________(.215%)

30. New Jersey Nets (30)____________________(.164%)

NBA Power Ranking (by Relative Winning %)

January 5, 2010

I objectively power ranked the National Basketball Association using a comparative technique I call “Relative Winning Percentage”.

What is “Relative Winning Percentage”?

“Relative Winning Percentage” is a pretty simple calculation and its done like this.  First I split each team’s schedule into home and road games.  Then I compare each team’s pythagorean winning percentage at home to the rest of the NBA’s pythagorean winning percentage at home against the very same opponents.  Then I subract the team average from the NBA average to get the team’s comparative difference.  Next I do the exact same thing for the team’s road schedule.  Then I average the two differences and add .500% to that average to get the team’s “Relative Winning Percentage”.

Basically, Relative Winning Percentage tells you how each team’s performance compares to the performance of the rest of the NBA against the same schedule.  Thus it accounts for location and for strength of opponent.  The new twist is the home/road 50/50 split.  I decided to add that twist because I realized that even if you account for homecourt advantage many NBA teams simply perform at different levels at home than they do on the road.  Realizing that, I wanted to give equal weight to both because I think that doing so gives a truer picture of team strength and, more importantly, a team’s likely playoff performance.

(Calculation Example:  The Bucks Pythagorean Home Winning % is .578%.  Playing the same home schedule, the rest of the NBA has a Pythagorean Home Winning % of .580%.  The Bucks Pythagorean Road Winning % is .319%.  Playing the same road schedule, the rest of the NBA has a Pythagorean Road Winning % of .433%.  Thus the Bucks are (-.002) at home and (-.114) on the road, which averages to (-.058).  Add .500 to that and you get the Bucks “Relative Winning Percentage” of  .442% ).

With that explanation, here is the NBA Power Ranking as of January 4, 2010.  In my next two posts I will rank each team separately according to home and road strength.

NBA POWER RANKING (using Relative Winning Percentage)

1. Cleveland Cavaliers__________(.676%)

2. Atlanta Hawks_______________(.673%)

3. Boston Celtics_______________(.666%)

4. LA Lakers___________________(.663%)

5. Orlando Magic_______________(.653%)

6. San Antonio Spurs____________(.649%)

7. Denver Nuggets______________(.642%)

8. Dallas Mavericks______________(.619%)

9. Phoenix Suns_________________(.613%)

10. Oklahoma City Thunder_______(.584%)

11. Houston Rockets______________(.571%)

12. Portland Trailblazers__________(.567%)

13. Utah Jazz_____________________(.552%)

14. Miami Heat___________________(.513%)

15. Memphis Grizzlies_____________(.491%)

16. Charlotte Bobcats_____________(.483%)

17. Toronto Raptors______________(.450%)

18. Sacramento Kings_____________(.446%)

19. Milwaukee Bucks______________(.442%)

20. New Orleans Hornets__________(.417%)

21. New York Knicks______________(.401%)

22. LA Clippers___________________(.399%)

23. Detroit Pistons________________(.392%)

24. Golden State Warriors__________(.389%)

25. Washington Wizards___________(.383%)

26. Philadelphia Sixers____________(.380%)

27. Chicago Bulls_________________(.359%)

28. Indiana Pacers________________(.346%)

29. Minnesota Timberwolves_______(.230%)

30. New Jersey Nets_______________(.208%)


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