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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

Sports Reference Welcomes Adam Wodon to Our Staff

Posted by sean on February 9, 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.

2 Comments | 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

Play Index Tools Now with Short Surveys & no Ads

Posted by sean on October 8, 2014

Since we've launched the various Play Index tools on our sites, we've struggled with the best way to monetize what we feel is the deepest and most powerful set of sports data tools anywhere. We know they are useful, our users, the teams, broadcast networks, and newspaper reporters tell us so.

On baseball, we charge an annual fee of $36, but our best guess is that the traffic and audience of the other sites would not be sufficient to make a subscription model worth our while. We have been running traditional banner ads on those pages, but they pay so little and the play index content is niche content (valuable, but niche content) so the traffic will never rise that high on the play index pages. So we have decided to remove all banner advertising and instead run Google consumer surveys on the non-baseball play index pages.

Here's how it works. The first time you run a report each day your results will be obscured and you will be asked to answer a 1-5 question survey. After you answer the survey, your requested report will be shown to you and you won't see another survey for that site on that browser for 24 hours (multi-question surveys are good for 48 hours). These surveys pay us around 5 cents per survey which, while it doesn't sound like much, is about 15 times what we would get from banner ads on those pages. Here is an FAQ if you are wondering how Google uses this information.

Also, if you find these gateway surveys a step too far, consider subscribing to our Ad-Free Access. Starting at $20/year you can surf every Sports Reference page ad and survey free.

If you are wondering what our play index tools are, give them a try. We think you'll enjoy them.
Play Index at Basketball-Reference.com
Play Index at Pro-Football-Reference.com
Play Index at Hockey-Reference.com
Play Index at Sports-Reference.com/cbb
Play Index at Sports-Reference.com/cfb

Comments Off | Posted in Advanced Stats, Announcement, Basketball-Reference.com, CBB at Sports Reference, CFB at Sports Reference, Hockey-Reference.com, Pro-Football-Reference.com

The Relationship Between Winning and Ticket Prices in College Football

Posted by TiqIQ Staff on September 12, 2014

By Dan Pizzuta

There's not many things in sports that can increase ticket prices on the secondary market like successful on-field performance. Generally the best teams have the highest ticket prices. However, early in the season some of the price points are still based on preseason expectations and on-field performance has not yet led to shifts in the market. That's especially true early in the college football season on the secondary market.

TiqIQ tracks the most average prices by school on the secondary market during the college football season with the TiqIQ Top 25. Of the schools with the 25 most expensive average prices, 12 are also currently in the Top 25 of SRS after two weeks of the season.

Through two games, the closest match between SRS and secondary market prices is Notre Dame. The Fighting Irish are ranked as the top team with a SRS of 56.99. Notre Dame football tickets are also the third most expensive on the secondary market with a $215 average price for 2014 home games. The University of Georgia is close to Notre Dame, ranking fourth in SRS and second on the secondary market as UGA football tickets have an average price of $219. The biggest disagreement between the two is Ohio State. Ohio State football tickets are the most expensive in the country with a $252 average price. Ohio State's average is 15 percent above the next school, however, they come in just 55th in SRS, 7.43 points above average.

Four of the top ten schools in SRS do not appear in the 25 most expensive schools on the secondary market. Of those four, only Michigan football tickets are the closest to cracking the Top 25. The Wolverines currently have the 26th highest average price in the country at $120. Home games on the Michigan football schedule are typically more expensive, but both high profile rivalry games against Notre Dame and Ohio State were scheduled on the road this season.

When it comes to average prices on the secondary market, there's not much of a difference between top offensive and defensive schools. Both eight of the top 25 schools in defensive and offensive SRS appear on the TiqIQ Top 25. The best defensive schools have a bit of an edge when the it comes to being top five units. Four of the top defensive teams in the TiqIQ Top 25 are in the top five in Defensive SRS. However only two of the eight offensive teams on the secondary market are top five in Offensive SRS--Georgia and Auburn.

Of the 25 most expensive schools on the secondary market, Auburn football tickets might be the best deal. The Tigers rank 14th on the TiqIQ Top 25 and third in SRS. They are only top secondary market school that rank in the top 25 in SRS for both offense and defense. For that type of balance, the $149 average price at Jordan Hare Stadium could be considered a steal.

 

Comments Off | Posted in Announcement, CFB at Sports Reference, Pro-Football-Reference.com

College Football Logos Added

Posted by Mike on September 11, 2014

Thanks to Chris Creamer and his wonderful site SportsLogos.net, we've added current logos to all 2014 school pages, as well as a new top 25 listing in the left column on the college football front page. Clicking the link below the logo on the school page will take you to the SportsLogos.net historical logos page for that team, where you can see historical logos, helmets, lettering, and more.

Comments Off | Posted in Announcement, CFB at Sports Reference

Your One-Stop Resource for 2014 College Football Data

Posted by Mike Lynch on August 29, 2014

With the 2014 college football season upon, just a few reminders on where to find info for this season:

If you have any questions about where to find something or if you encounter any issues, please let us know here.

2 Comments | Posted in Announcement, CFB at Sports Reference, Data, Play Index, Uncategorized

Surf Sports Reference Faster – Buy Ad-Free Access on all sites

Posted by sean on June 17, 2014

We like to keep our sites really, really fast and obsess over as many performance details as we can. Unfortunately one area where we have little control is in the performance of our advertisements as companies of our size typically outsource this task. We rely on ads for 85% of our revenue, but we are aware that some of these ads degrade our service.

We have decided to launch a new ad-free service. It's available on all of our sites and for $20 you can surf all of our sites ad-free. To sign up see the "AD FREE" link that now appears at the top of every page.

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Using this service will make your surfing experience much faster and will continue to support our site.

Sign up via Baseball-Reference.com

9 Comments | Posted in Announcement, Baseball-Reference.com, Basketball-Reference.com, CBB at Sports Reference, CFB at Sports Reference, Hockey-Reference.com, Olympics at S-R, Pro-Football-Reference.com

Maintenance Downtime (a few minutes), afternoon of May 14, 2014

Posted by admin on May 13, 2014

Due to a need to replace a faulty power supply the sites will be down for hopefully just a few minutes tomorrow afternoon as the power supply is being replace. The work is scheduled to occur sometime between 1 and 3 pm ET and should affect only our CFB, CBB and Olympics sites and this blog. Should a longer outage be necessary or any additional sites be affected, we will post any updates to our twitter accounts.

Comments Off | Posted in Announcement, Baseball-Reference.com, Basketball-Reference.com, CBB at Sports Reference, CFB at Sports Reference, expire2d, Hockey-Reference.com, Olympics at S-R, Pro-Football-Reference.com

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