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.