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SRS Calculation Details

Posted by Mike Lynch on March 3, 2015

One of the more common subjects for queries we receive at Sports-Reference is our SRS (Simple Rating System) figures. For some background, the first of our sites to add SRS was Pro-Football-Reference, when Doug Drinen added it to the site in 2006 and provided this excellent primer. The important thing to know is that SRS is a rating that takes into account average point differential and strength of schedule. For instance, the 2006-07 Spurs won games by an average of 8.43 points per game and played a schedule with opponents that were 0.08 points worse than average, giving them an SRS of 8.35. This means they were 8.35 points better than an average team. An average team would have an SRS of 0.0. The calculation can be complicated, but the premise is simple and it produces easily interpreted results.

However, there are some variations in the way we calculate SRS across our various sites. We'll break down these differences below.

Pro-Football-Reference.com SRS: PFR's SRS is unique in that a home-field advantage is included as a part of the calculation because of the short schedule compared to the other sports (we don't want a team to look relatively weak at the halfway point because they've only played 3 of their first 8 at home, for instance). This HFA fluctuates yearly based on game results, but it is generally somewhere between 2 and 3 points (2006 being an outlier, as you'll see). Below is a look at the HFA numbers we have used since 2001. If you'd like to calculate these HFAs yourself, just sum up every team's home point differential and then divide by the total number of games played across the league that season. This data can easily be found in the Play Index for each season:

  • 2001: 2.0081
  • 2002: 2.2461
  • 2003: 3.5547
  • 2004: 2.5078
  • 2005: 3.6484
  • 2006: 0.8477
  • 2007: 2.8672
  • 2008: 2.5586
  • 2009: 2.2070
  • 2010: 1.8945
  • 2011: 3.2656
  • 2012: 2.4336
  • 2013: 3.1055
  • 2014: 2.4883

College Football SRS: Our CFB SRS does not contain a home-field advantage element, but it does have some other quirks. Most importantly, we have capped the margin of victory considered for the formula. Due to the number of mismatches seen in college football, the maximum point differential a team can be credited with in a game is 24. We also credit all wins as a minimum of plus-7 margin of victory (so if you win by 1 point, it's treated the same as a 7-point win). The same logic is applied to losses, as well. One other wrinkle for CFB is that all non-major opponents are included as one team for the sake of the ratings.

College Basketball SRS: SRS for college hoops is straight forward (no HFA & no adjusted MOV), but one item to note is that games against non-major opponents are not counted in our calculations.

MLB, NBA & NHL: All of these SRS calculations are straight forward with no adjustments for HFA and no capping of MOV. It should be noted, however, that no special consideration is given for extra-innings, overtimes or shootouts, either.

We'll close with a quick rundown of the various merits and weaknesses of SRS, from Drinen's original 2006 post. These bullet points were created to describe the system used for NFL SRS, but many of the strengths and weaknesses can applied to the other sports, as well:

  • The numbers it spits out are easy to interpret - if Team A's rating is 3 bigger than Team B's, this means that the system thinks Team A is 3 points better than Team B. With most ranking algorithms, the numbers that come out have no real meaning that can be translated into an English sentence. With this system, the units are easy to understand.
  • It is a predictive system rather than a retrodictive system - this is a very important distinction. You can use these ratings to answer the question: which team is stronger? I.e. which team is more likely to win a game tomorrow? Or you can use them to answer the question: which of these teams accomplished more in the past? Some systems answer the first questions more accurately; they are called predictive systems. Others answer the latter question more accurately; they are called retrodictive systems. As it turns out, this is a pretty good predictive system. For the reasons described below, it is not a good retrodictive system.
  • It weights all games equally - every football fan knows that the Colts' week 17 game against Arizona was a meaningless exhibition, but the algorithm gives it the same weight as all the rest of the games.
  • It weights all points equally, and therefore ignores wins and losses - take a look at the Colts season. If you take away 10 points in week 3 and give them back 10 points in week 4, you've just changed their record, but you haven't changed their rating at all. If you take away 10 points in week 3 and give back 20 points in week 4, you have made their record worse but their rating better. Most football fans put a high premium on the few points that move you from a 3-point loss to a 3-point win and almost no weight on the many points that move you from a 20-point win to a 50-point win.
  • It is easily impressed by blowout victories - this system thinks a 50-point win and a 10-point loss is preferable to two 14-point wins. Most fans would disagree with that assessment.
  • It is slightly biased toward offensive-minded teams - because it considers point margins instead of point ratios, it treats a 50-30 win as more impressive than a 17-0 win. Again, this is an assessment that most fans would disagree with.
  • This should go without saying, but - I'll say it anyway. The system does not take into account injuries, weather conditions, yardage gained, the importance of the game, whether it was a Monday Night game or not, whether the quarterback's grandmother was sick, or anything else besides points scored and points allowed.

 

2 Comments | Posted in Announcement, Baseball-Reference.com, Basketball-Reference.com, CBB at Sports Reference, CFB at Sports Reference, Data, FAQ, Features, Hockey-Reference.com, Pro-Football-Reference.com, SRS, Stat Questions, Statgeekery, Uncategorized

Where Does Florida State Rank Entering the BCS Championship Game?

Posted by Neil on December 9, 2013

Chase asked where FSU's +42.3 pre-bowl PPG differential ranked among all BCS-bowl teams historically, so I thought I'd run a quick database search:

Year School Pre-Bowl MOV Bowl
2013 Florida State (acc) +42.3 BCSCG (vs. Auburn)
2005 Texas (big-12) +36.3 Rose (W 41-38 vs. Southern California)
2001 Miami (FL) (big-east) +33.8 Rose (W 37-14 vs. Nebraska)
2008 Florida (sec) +32.3 BCSCG (W 24-14 vs. Oklahoma)
2000 Florida State (acc) +32.2 Orange (L 2-13 vs. Oklahoma)
2013 Baylor (big-12) +32.1 Fiesta (vs. Central Florida)
2010 Texas Christian (mwc) +31.9 Rose (W 21-19 vs. Wisconsin)
2010 Oregon (pac-10) +30.9 BCSCG (L 19-22 vs. Auburn)
1999 Virginia Tech (big-east) +30.8 Sugar (L 29-46 vs. Florida State)
2003 Oklahoma (big-12) +30.3 Sugar (L 14-21 vs. Louisiana State)
2008 Southern California (pac-10) +29.8 Rose (W 38-24 vs. Penn State)
2001 Florida (sec) +29.7 Orange (W 56-23 vs. Maryland)
2008 Oklahoma (big-12) +29.5 BCSCG (L 14-24 vs. Florida)
2012 Oregon (pac-12) +28.8 Fiesta (W 35-17 vs. Kansas State)
2005 Southern California (pac-10) +28.7 Rose (L 38-41 vs. Texas)
2007 Kansas (big-12) +28.3 Orange (W 24-21 vs. Virginia Tech)
2009 Texas Christian (mwc) +28.3 Fiesta (L 10-17 vs. Boise State)
2011 Louisiana State (sec) +27.9 BCSCG (L 0-21 vs. Alabama)
2012 Alabama (sec) +27.8 BCSCG (W 42-14 vs. Notre Dame)
2008 Penn State (big-ten) +27.8 Rose (L 24-38 vs. Southern California)
2011 Wisconsin (big-ten) +27.6 Rose (L 38-45 vs. Oregon)
2013 Alabama (sec) +27.4 Sugar (vs. Oklahoma)
2000 Miami (FL) (big-east) +27.2 Sugar (W 37-20 vs. Florida)
2011 Alabama (sec) +27.2 BCSCG (W 21-0 vs. Louisiana State)
2009 Boise State (wac) +26.5 Fiesta (W 17-10 vs. Texas Christian)
2010 Ohio State (big-ten) +26.1 Sugar (W 31-26 vs. Arkansas)
2006 Ohio State (big-ten) +25.9 BCSCG (L 14-41 vs. Florida)
2004 Utah (mwc) +25.6 Fiesta (W 35-7 vs. Pittsburgh)
2009 Texas (big-12) +25.5 BCSCG (L 21-37 vs. Alabama)
2008 Texas (big-12) +25.3 Fiesta (W 24-21 vs. Ohio State)
2007 Oklahoma (big-12) +25.2 Fiesta (L 28-48 vs. West Virginia)
1998 Ohio State (big-ten) +25.1 Sugar (W 24-14 vs. Texas A&M)
2013 Ohio State (big-ten) +25.0 Orange (vs. Clemson)
2012 Florida State (acc) +24.8 Orange (W 31-10 vs. Northern Illinois)
2004 Southern California (pac-10) +24.3 Orange (W 55-19 vs. Oklahoma)
2003 Louisiana State (sec) +24.2 Sugar (W 21-14 vs. Oklahoma)
2006 Boise State (wac) +23.8 Fiesta (W 43-42 vs. Oklahoma)
2002 Miami (FL) (big-east) +23.8 Fiesta (L 24-31 vs. Ohio State)
2011 Oklahoma State (big-12) +23.5 Fiesta (W 41-38 vs. Stanford)
2002 Oklahoma (big-12) +23.5 Rose (W 34-14 vs. Washington State)
2003 Southern California (pac-10) +23.4 Rose (W 28-14 vs. Michigan)
2011 Stanford (pac-12) +23.3 Fiesta (L 38-41 vs. Oklahoma State)
2009 Florida (sec) +23.2 Sugar (W 51-24 vs. Cincinnati)
2000 Oklahoma (big-12) +23.0 Orange (W 13-2 vs. Florida State)
2010 Wisconsin (big-ten) +22.8 Rose (L 19-21 vs. Texas Christian)
2011 Oregon (pac-12) +22.5 Rose (W 45-38 vs. Wisconsin)
2010 Stanford (pac-10) +22.5 Orange (W 40-12 vs. Virginia Tech)
1999 Wisconsin (big-ten) +22.5 Rose (W 17-9 vs. Stanford)
2004 Oklahoma (big-12) +22.4 Orange (L 19-55 vs. Southern California)
2006 Louisville (big-east) +22.3 Orange (W 24-13 vs. Wake Forest)
2003 Kansas State (big-12) +22.3 Fiesta (L 28-35 vs. Ohio State)
2004 Auburn (sec) +22.3 Sugar (W 16-13 vs. Virginia Tech)
2007 Hawaii (wac) +22.0 Sugar (L 10-41 vs. Georgia)
2012 Northern Illinois (mac) +21.8 Orange (L 10-31 vs. Florida State)
1999 Nebraska (big-12) +21.8 Fiesta (W 31-21 vs. Tennessee)
2007 West Virginia (big-east) +21.7 Fiesta (W 48-28 vs. Oklahoma)
2001 Nebraska (big-12) +21.7 Rose (L 14-37 vs. Miami (FL))
1999 Florida State (acc) +21.6 Sugar (W 46-29 vs. Virginia Tech)
2007 Ohio State (big-ten) +21.3 BCSCG (L 24-38 vs. Louisiana State)
2003 Michigan (big-ten) +21.3 Rose (L 14-28 vs. Southern California)
1998 Wisconsin (big-ten) +21.1 Rose (W 38-31 vs. UCLA)
2002 Iowa (big-ten) +20.8 Orange (L 17-38 vs. Southern California)
2009 Alabama (sec) +20.7 BCSCG (W 37-21 vs. Texas)
2006 Louisiana State (sec) +20.6 Sugar (W 41-14 vs. Notre Dame)
1998 Florida State (acc) +20.6 Fiesta (L 16-23 vs. Tennessee)
2008 Utah (mwc) +20.2 Sugar (W 31-17 vs. Alabama)
2004 Virginia Tech (acc) +19.7 Sugar (L 13-16 vs. Auburn)
2012 Kansas State (big-12) +19.6 Fiesta (L 17-35 vs. Oregon)
1998 Tennessee (sec) +19.6 Fiesta (W 23-16 vs. Florida State)
2009 Cincinnati (big-east) +19.1 Sugar (L 24-51 vs. Florida)
2013 Clemson (acc) +19.1 Orange (vs. Ohio State)
2007 Louisiana State (sec) +19.1 BCSCG (W 38-24 vs. Ohio State)
2004 Texas (big-12) +18.8 Rose (W 38-37 vs. Michigan)
2005 Penn State (big-ten) +18.7 Orange (W 26-23 vs. Florida State)
2010 Auburn (sec) +18.2 BCSCG (W 22-19 vs. Oregon)
2008 Alabama (sec) +18.2 Sugar (L 17-31 vs. Utah)
1998 Syracuse (big-east) +18.1 Orange (L 10-31 vs. Florida)
2005 Ohio State (big-ten) +17.7 Fiesta (W 34-20 vs. Notre Dame)
2000 Florida (sec) +17.7 Sugar (L 20-37 vs. Miami (FL))
1998 Florida (sec) +17.6 Orange (W 31-10 vs. Syracuse)
2002 Georgia (sec) +17.3 Sugar (W 26-13 vs. Florida State)
2009 Ohio State (big-ten) +17.1 Rose (W 26-17 vs. Oregon)
2013 Michigan State (big-ten) +17.1 Rose (vs. Stanford)
2011 Michigan (big-ten) +17.0 Sugar (W 23-20 vs. Virginia Tech)
2003 Florida State (acc) +17.0 Orange (L 14-16 vs. Miami (FL))
2002 Southern California (pac-10) +17.0 Orange (W 38-17 vs. Iowa)
2002 Ohio State (big-ten) +16.9 Fiesta (W 31-24 vs. Miami (FL))
1999 Tennessee (sec) +16.8 Fiesta (L 21-31 vs. Nebraska)
2010 Virginia Tech (acc) +16.5 Orange (L 12-40 vs. Stanford)
2012 Notre Dame (independent) +16.4 BCSCG (L 14-42 vs. Alabama)
2001 Maryland (acc) +16.4 Orange (L 23-56 vs. Florida)
2013 Auburn (sec) +16.2 BCSCG (vs. Florida State)
2006 Michigan (big-ten) +15.6 Rose (L 18-32 vs. Southern California)
2006 Southern California (pac-10) +15.4 Rose (W 32-18 vs. Michigan)
2006 Florida (sec) +15.4 BCSCG (W 41-14 vs. Ohio State)
2007 Southern California (pac-10) +15.3 Rose (W 49-17 vs. Illinois)
2005 West Virginia (big-east) +15.3 Sugar (W 38-35 vs. Georgia)
2008 Ohio State (big-ten) +15.1 Fiesta (L 21-24 vs. Texas)
2013 Stanford (pac-12) +14.6 Rose (vs. Michigan State)
2010 Arkansas (sec) +14.6 Sugar (L 26-31 vs. Ohio State)
2005 Notre Dame (independent) +14.5 Fiesta (L 20-34 vs. Ohio State)
2005 Georgia (sec) +14.5 Sugar (L 35-38 vs. West Virginia)
2010 Oklahoma (big-12) +14.5 Fiesta (W 48-20 vs. Connecticut)
2000 Oregon State (pac-10) +14.2 Fiesta (W 41-9 vs. Notre Dame)
2009 Oregon (pac-10) +14.1 Rose (L 17-26 vs. Ohio State)
2006 Oklahoma (big-12) +14.1 Fiesta (L 42-43 vs. Boise State)
2007 Virginia Tech (acc) +13.8 Orange (L 21-24 vs. Kansas)
2012 Florida (sec) +13.8 Sugar (L 23-33 vs. Louisville)
2003 Miami (FL) (big-east) +13.6 Orange (W 16-14 vs. Florida State)
2013 Central Florida (american) +13.6 Fiesta (vs. Baylor)
1998 UCLA (pac-10) +13.0 Rose (L 31-38 vs. Wisconsin)
2002 Washington State (pac-10) +12.9 Rose (L 14-34 vs. Oklahoma)
2001 Oregon (pac-10) +12.2 Fiesta (W 38-16 vs. Colorado)
2012 Wisconsin (big-ten) +11.7 Rose (L 14-20 vs. Stanford)
2000 Purdue (big-ten) +11.4 Rose (L 24-34 vs. Washington)
2011 Virginia Tech (acc) +11.3 Sugar (L 20-23 vs. Michigan)
2012 Stanford (pac-12) +11.0 Rose (W 20-14 vs. Wisconsin)
2007 Georgia (sec) +10.9 Sugar (W 41-10 vs. Hawaii)
2002 Florida State (acc) +10.8 Sugar (L 13-26 vs. Georgia)
2001 Illinois (big-ten) +10.7 Sugar (L 34-47 vs. Louisiana State)
2000 Notre Dame (independent) +10.7 Fiesta (L 9-41 vs. Oregon State)
2013 Oklahoma (big-12) +10.5 Sugar (vs. Alabama)
2009 Georgia Tech (acc) +10.5 Orange (L 14-24 vs. Iowa)
1999 Michigan (big-ten) +10.3 Orange (W 35-34 vs. Alabama)
1998 Texas A&M (big-12) +10.1 Sugar (L 14-24 vs. Ohio State)
2006 Notre Dame (independent) +10.0 Sugar (L 14-41 vs. Louisiana State)
2000 Washington (pac-10) +9.7 Rose (W 34-24 vs. Purdue)
2001 Colorado (big-12) +9.7 Fiesta (L 16-38 vs. Oregon)
1999 Alabama (sec) +9.5 Orange (L 34-35 vs. Michigan)
2007 Illinois (big-ten) +9.3 Rose (L 17-49 vs. Southern California)
2011 West Virginia (big-east) +8.7 Orange (W 70-33 vs. Clemson)
2001 Louisiana State (sec) +8.6 Sugar (W 47-34 vs. Illinois)
2004 Michigan (big-ten) +8.4 Rose (L 37-38 vs. Texas)
2005 Florida State (acc) +7.8 Orange (L 23-26 vs. Penn State)
2009 Iowa (big-ten) +7.6 Orange (W 24-14 vs. Georgia Tech)
2006 Wake Forest (acc) +7.5 Orange (L 13-24 vs. Louisville)
2011 Clemson (acc) +7.5 Orange (L 33-70 vs. West Virginia)
2012 Louisville (big-east) +7.2 Sugar (W 33-23 vs. Florida)
2003 Ohio State (big-ten) +7.2 Fiesta (W 35-28 vs. Kansas State)
2008 Cincinnati (big-east) +7.2 Orange (L 7-20 vs. Virginia Tech)
2010 Connecticut (big-east) +7.1 Fiesta (L 20-48 vs. Oklahoma)
2004 Pittsburgh (big-east) +5.9 Fiesta (L 7-35 vs. Utah)
1999 Stanford (pac-10) +5.6 Rose (L 9-17 vs. Wisconsin)
2008 Virginia Tech (acc) +4.8 Orange (W 20-7 vs. Cincinnati)

6 Comments | Posted in Advanced Stats, Announcement, CFB at Sports Reference, History, Pro-Football-Reference.com, SRS, Stat Questions, Statgeekery, Trivia

Yearly Schedule-Adjusted Offensive and Defensive Ratings

Posted by Neil on June 6, 2012

As part of an ESPN article I was writing, I had to calculate SRS-style schedule-adjusted regular-season offensive and defensive ratings for every team since 1985-86, much like I computed in past seasons for the BBR Rankings.

Since I created that dataset anyway, I thought I might as well post it here for posterity's sake (and as a handy reference for people in the future):

6 Comments | Posted in Advanced Stats, Announcement, Basketball-Reference.com, Data, SRS

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