3rd March 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.
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 | 2 Comments »
27th February 2015
Posted in Announcement, Baseball-Reference.com, Basketball-Reference.com, CBB at Sports Reference, CFB at Sports Reference, expire21d, Hockey-Reference.com, Olympics at S-R, Pro-Football-Reference.com, Statgeekery | Comments Off on Hiring: Analytics Consultant, Posted Feb 27, 2015
16th February 2015
We're happy to announce a new promotion that allows users to get a year-long Play Index subscription (or renewal) for only $15, which is less than half of the normal price ($36).
All you have to do is make a deposit of at least $15 at this DraftKings link. Please note that this promotion is only for first-time DraftKings users. If you're unfamiliar with DraftKings, it is a site which offers daily fantasy games for cash in all of the major North American sports leagues, plus some others. Once you make your deposit via that link, we will be notified and send you an email with a coupon code for the year-long Play Index subscription.
The Play Index is our baseball research tool, which allows subscribers to make custom searches through 100 years of box scores, splits, streaks and events. You can also make custom searches for any season stat line in MLB history. A full description of the Play Index and its tools can be found here. It is the most powerful baseball research tool available to the public.
If you're already a Play Index subscriber, you can still take advantage of this offer. Your Play Index subscription will simply be extended one full year from its current expiration date.
Posted in Announcement, Baseball-Reference.com, Play Index | Comments Off on Get Free Play Index Subscription with $15 Deposit on DraftKings
11th February 2015
On Thursday, February 12th around 9:30am we'll be switching servers for Baseball-Reference.com (moving from unitas to tris). Should be no downtime #dalemurphywilling.
Posted in Announcement, Baseball-Reference.com, expire2d | Comments Off on Baseball-Reference.com Server Move, 9:30am ET Thursday
9th February 2015
Adam Wodon has joined Sports Reference today as a Managing Director for Hockey Reference. Adam will be working out of our Philadelphia office as our staff size has now risen to six. Adam brings a great deal of development experience and hockey knowledge to Sports Reference. Adam is the founder and managing editor of College Hockey News. Adam is an Isles fan through and through and also supports the Mets, Jets, and Nets making him the first diehard National League fan on staff. Adam is also on twitter at (@chn_AdamWodon).
Hans VanSlooten (@CantPitch) who had been working on the hockey site for the last 14 months will be taking over primary day-to-day development of Baseball-Reference.com.
Posted in Announcement, Baseball-Reference.com, Basketball-Reference.com, CBB at Sports Reference, CFB at Sports Reference, Expire30d, Hockey-Reference.com, Olympics at S-R, Pro-Football-Reference.com | 2 Comments »
6th February 2015
We have recently added Cuban statistics and Arizona Fall League stats. Our other new addition is statistics for the Dominican, Venezuelan, Puerto Rican & Mexican Pacific Winter Leagues.
These leagues can all be accessed via our Minor Leagues section. On player's minors pages, the abbreviations are DOWL (Dominican), VEWL (Venezuelan), PRWL (Puerto Rican) & MXPW (Mexican Pacific). These leagues also feature batting leaderboards, so you can find outstanding performances like Kendrys Morales batting .404, and pitching leaderboards.
Posted in Announcement, Baseball-Reference.com, Data | Comments Off on Winter League Statistics Added
6th February 2015
Yesterday we announced that we have added Cuban statistics to the site. Today, we are happy to announce that we have added Arizona Fall League statistics to the site from 2005-13 (with 2014 coming soon).
Statistics from this league can be seen on a player's minor league page. Here is Mike Trout's, for instance. The Arizona Fall League is coded as AZFL on these pages. From the league page, you can navigate to various batting leaderboards and pitching leaderboards. The AFL is accessible from our minor leagues home page.
Posted in Announcement, Baseball-Reference.com, Data | 2 Comments »
5th February 2015
We are happy to announce that we have added Cuban National Series statistics from 1997-98 to 2013-14 thanks to the efforts of Brian Cartwright. First thing's first, though. You should go ahead and gawk at Jose Abreu's Cuban stats. That's right, he hit .453 in 2010 with 1.583 OPS. Those both led the league, but his 33 HR merely tied Yoenis Cespedes for first.
These statistics can be navigated to via our Minor Leagues section here. Once in the minors section, look for Foreign leagues and select Cuban National Series. You can select a season and access batting leaders & pitching leaders from there.
Alternately, if you just want to find Cuban stats for an MLB player like Yasiel Puig, just go to the Minors tab from his player page. Or you can use the search form to go right to the page of a hot prospect like Yoan Moncada. On a player's minor league stats page, the Cuban statistics will show up with the league abbreviation CNS like in the image of Erisbel Arruebarrena's page below.
We hope you enjoy this new feature. We would also like to note that we will be adding statistics from the current season once is it completed.
Posted in Announcement, Baseball-Reference.com, Data, Features | 5 Comments »
19th January 2015
The Greg Spira Baseball Research Award Committee is seeking nominations for the third annual Greg Spira Baseball Research Award. The nomination period opened on January 16 and will remain open through February 15. For more information, please visit www.spiraaward.org
Posted in Announcement, Baseball-Reference.com | Comments Off on Seeking Nominations for 2015 Greg Spira Award
6th January 2015
With the announcement of the 2015 Baseball Hall of Fame class this afternoon, here are some useful links from around the site:
Please enjoy these features as you debate with your friends today.
Posted in Announcement, Awards, Baseball-Reference.com, Data, Hall of Fame | 13 Comments »