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The Simple Rating System

Posted by Justin Kubatko on March 10, 2008

You may have noticed that I added something called "SRS" to the team and league pages. SRS stands for Simple Rating System, and I stole the idea from my colleague at Pro-Football-Reference.com, Doug Drinen (who probably stole it from someone else). Anyway, Doug has written a really nice explanation of the system, so rather than reinvent the wheel I'll ask you to read Doug's primer. OK, go ahead...

Back? Good. One thing I really like about the SRS is that the ratings have a very nice interpretation. For example, here are the top five teams in the NBA (based on the SRS) in 2006-07:

Team                      Margin    SOS    SRS

San Antonio Spurs           8.43  -0.08   8.35  
Dallas Mavericks            7.22   0.06   7.28  
Phoenix Suns                7.30  -0.03   7.27  
Houston Rockets             4.85   0.18   5.04  
Chicago Bulls               5.01  -0.49   4.52  

Let's use the Spurs as an example. The Spurs defeated their opponents by an average margin of 8.43 points. However, their opponents were, on average, 0.08 points worse than average. After adjusting for their schedule, we estimate that San Antonio was 8.43 - 0.08 = 8.35 points better than average.

Comparing one team to another is very easy. The Spurs rating last season was 8.35. The Cleveland Cavaliers, the team they beat in the NBA Finals, had a rating of 3.33. So the SRS leads us to believe that the Spurs were 8.35 - 3.33 = 5.02 points better than the Cavs last season. If we assume a 3-point home-court advantage, then the system would have favored the Spurs by 2.02 points in Cleveland and by 8.02 points in San Antonio. (It's interesting to note that in their four-game sweep of the Cavs, the Spurs won by an average of 10 points in San Antonio and 2 points in Cleveland.)

Some interesting lists can be made using the SRS. For example, here are the top teams based on the SRS along with the league champion for each of the BAA/NBA's past 61 seasons:

Season   Lg     SRS Leader                 SRS  Champion                          SRS
1946-47  BAA    Washington Capitols       8.96  Philadelphia Warriors            3.16
1947-48  BAA    Baltimore Bullets         3.70  Baltimore Bullets                3.70
1948-49  BAA    Minneapolis Lakers        6.81  Minneapolis Lakers               6.81
1949-50  NBA    Minneapolis Lakers        8.25  Minneapolis Lakers               8.25
1950-51  NBA    Minneapolis Lakers        4.79  Rochester Royals                 2.54
1951-52  NBA    Minneapolis Lakers        5.28  Minneapolis Lakers               5.28
1952-53  NBA    Minneapolis Lakers        5.53  Minneapolis Lakers               5.53
1953-54  NBA    Syracuse Nationals        4.26  Minneapolis Lakers               2.70
1954-55  NBA    Fort Wayne Pistons        2.01  Syracuse Nationals               1.23
1955-56  NBA    Philadelphia Warriors     3.82  Philadelphia Warriors            3.82
1956-57  NBA    Boston Celtics            4.79  Boston Celtics                   4.79
1957-58  NBA    Boston Celtics            5.03  St. Louis Hawks                  0.82
1958-59  NBA    Boston Celtics            5.84  Boston Celtics                   5.84
1959-60  NBA    Boston Celtics            7.62  Boston Celtics                   7.62
1960-61  NBA    Boston Celtics            4.93  Boston Celtics                   4.93
1961-62  NBA    Boston Celtics            8.25  Boston Celtics                   8.25
1962-63  NBA    Boston Celtics            6.38  Boston Celtics                   6.38
1963-64  NBA    Boston Celtics            6.93  Boston Celtics                   6.93
1964-65  NBA    Boston Celtics            7.48  Boston Celtics                   7.48
1965-66  NBA    Boston Celtics            4.34  Boston Celtics                   4.34
1966-67  NBA    Philadelphia 76ers        8.50  Philadelphia 76ers               8.50
1967-68  NBA    Philadelphia 76ers        7.96  Boston Celtics                   3.87
1968-69  NBA    New York Knickerbockers   5.48  Boston Celtics                   5.35
1969-70  NBA    New York Knickerbockers   8.42  New York Knickerbockers          8.42
1970-71  NBA    Milwaukee Bucks          11.91  Milwaukee Bucks                 11.91
1971-72  NBA    Los Angeles Lakers       11.65  Los Angeles Lakers              11.65
1972-73  NBA    Los Angeles Lakers        8.18  New York Knickerbockers          6.07
1973-74  NBA    Milwaukee Bucks           7.61  Boston Celtics                   3.42
1974-75  NBA    Washington Bullets        6.54  Golden State Warriors            2.86
1975-76  NBA    Golden State Warriors     6.23  Boston Celtics                   2.24
1976-77  NBA    Portland Trail Blazers    5.39  Portland Trail Blazers           5.39
1977-78  NBA    Portland Trail Blazers    5.92  Washington Bullets               0.82
1978-79  NBA    San Antonio Spurs         4.97  Seattle Supersonics              2.69
1979-80  NBA    Boston Celtics            7.37  Los Angeles Lakers               5.43
1980-81  NBA    Philadelphia 76ers        7.76  Boston Celtics                   6.05
1981-82  NBA    Boston Celtics            6.35  Los Angeles Lakers               4.37
1982-83  NBA    Philadelphia 76ers        7.53  Philadelphia 76ers               7.53
1983-84  NBA    Boston Celtics            6.42  Boston Celtics                   6.42
1984-85  NBA    Milwaukee Bucks           6.70  Los Angeles Lakers               6.48
1985-86  NBA    Boston Celtics            9.06  Boston Celtics                   9.06
1986-87  NBA    Los Angeles Lakers        8.32  Los Angeles Lakers               8.32
1987-88  NBA    Boston Celtics            6.15  Los Angeles Lakers               4.81
1988-89  NBA    Cleveland Cavaliers       7.95  Detroit Pistons                  6.24
1989-90  NBA    Phoenix Suns              7.09  Detroit Pistons                  5.41
1990-91  NBA    Chicago Bulls             8.57  Chicago Bulls                    8.57
1991-92  NBA    Chicago Bulls            10.07  Chicago Bulls                   10.07
1992-93  NBA    Seattle Supersonics       6.66  Chicago Bulls                    6.19
1993-94  NBA    Seattle Supersonics       8.68  Houston Rockets                  4.19
1994-95  NBA    Seattle Supersonics       7.91  Houston Rockets                  2.32
1995-96  NBA    Chicago Bulls            11.80  Chicago Bulls                   11.80
1996-97  NBA    Chicago Bulls            10.70  Chicago Bulls                   10.70
1997-98  NBA    Chicago Bulls             7.24  Chicago Bulls                    7.24
1998-99  NBA    San Antonio Spurs         7.12  San Antonio Spurs                7.12
1999-00  NBA    Los Angeles Lakers        8.41  Los Angeles Lakers               8.41
2000-01  NBA    San Antonio Spurs         7.92  Los Angeles Lakers               3.74
2001-02  NBA    Sacramento Kings          7.61  Los Angeles Lakers               7.15
2002-03  NBA    Dallas Mavericks          7.91  San Antonio Spurs                5.65
2003-04  NBA    San Antonio Spurs         7.51  Detroit Pistons                  5.04
2004-05  NBA    San Antonio Spurs         7.84  San Antonio Spurs                7.84
2005-06  NBA    San Antonio Spurs         6.69  Miami Heat                       3.59
2006-07  NBA    San Antonio Spurs         8.35  San Antonio Spurs                8.35

Some random observations:

  • The SRS leader has been the league champion 33 times (54%).
  • The 1970-71 Milwaukee Bucks had the highest SRS of all time, 11.91 in 1970-71. The Bucks went 66-16 in the regular season (with a record point differential of 11.6 points per game) and won the NBA title, losing just two games in the playoffs. (It should be noted that three expansion teams debuted in the 1970-71 season.)
  • The league champion with the worst SRS was the 1957-58 St. Louis Hawks (0.82).
  • The Celtics have had the best SRS 15 times, followed by the Lakers (9 times), the Spurs (7 times), and the Bulls (5 times).

You get the point. Anyway, like I said earlier you can make some interesting lists using the SRS, and in the future I hope to share some more of them with you.

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