# Archive for the 'Basketball-Reference.com' Category

## SRS Calculation Details

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.

## Hiring: Analytics Consultant, Posted Feb 27, 2015

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

11th February 2015

Just a note that we have added Box Plus/Minus (BPM) to our College Basketball site this week.

As outlined in its introduction to Basketball Reference, BPM is an advanced stat intended to measure a player's total contribution as reflected by advanced, context-dependent box-score metrics like USG% and AST%. It was developed for the NBA using regression techniques against a 14-year-long sample of historical Regularized Adjusted Plus-Minus (RAPM) data. BPM estimates the number of points contributed by a player greater or less than an average player, per 100 team possessions.

We're able to calculate BPM for seasons dating back to 2010-11 and it can be found initially on player pages in the 'Advanced' table, on our school season pages, also in the 'Advanced' table, and we've also added several advanced stats - including PER, Win Shares, and BPM - to the conference registers, along the right side of that page. (see below image). However, the best way to view BPM, as a sorted leaderboard, or according to any other criteria - is to use our Play Index search tools.

Again, our thanks to the creator of BPM, Daniel Myers, and to those whose work serves as a component. The methodology and logic of Box Plus/Minus (BPM) is discussed in our About section, and please note the section specifically for the NCAA.

(Note that the 'Advanced' tables on the player and schools pages have changed just a little, to accommodate the new stats. Individual ORtg and DRtg have been moved to the 'Per 100 Possessions' tables and Points Produced - the main component of ORtg - has been moved further to the left on the 'Advanced' table.)

* We have published BPM but not VORP for college basketball, unlike the NBA.  Value over Replacement Player (VORP) owes its meaning and derivation to a market with salaried players and teams on an equal footing, and thus an easy-to-establish theoretical "replacement level", which doesn't exist or make sense for the NCAA.

## Sports Reference Welcomes Adam Wodon to Our Staff

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.

## Box Plus Minus/VORP for the Playoffs

9th February 2015

Playoff Box Plus/Minus (BPM)

We're now able to calculate Box Plus/Minus (BPM) and Value Over Replacement Player (VORP) for the playoffs, by extending the methodology used for the regular season, and calculating a team efficiency rating based on performance in the playoffs, adjusted for strength of playoff lineups (by using playoffs minute distributions and regular season BPM ratings). These ratings are interesting in themselves, and reflect some of the great playoffs runs - the 1996 Bulls' rating was +19.3, and the 2001 Lakers were +20.1.

The BPM figures themselves reflect the best individual playoff performances. LeBron's 2009 BPM of 18.2 is tops by a large margin, followed by Kareem's 1977 run and then the Jordan playoffs from 1989-1991.

(For a detailed explanation and further discussion see the "Playoff Box Plus/Minus and VORP" section of the write-up.)

Playoff VORP (and Pro-Rating the Regular Season)

As well as BPM, we can now calculate VORP for the playoff season. (If you need a refresher on VORP as a concept, please visit the original write-up when we introduced it to Basketball Reference). We calculate VORP for the playoffs similarly to the regular season - that is, [BPM - (-2.0)] * (% of minutes played) - and it should be interpreted identically. Again, that's as the number of points the player has produced over a replacement player, per 100 team possessions.  The significance of VORP compared to BPM is that it's accumulative, rather than a rate stat, and thus accounts more literally for value provided, weighted as it is by minutes played, and expressed on a per-82 game basis*.

(* - Yes, this is new. We are now pro-rating VORP based on the number of games that a team has played during the regular season, and doing the same for the playoffs. One point of VORP is one point of full season team efficiency differential. This affects partial seasons, strike-shortened seasons, and the playoffs.  This has significance for the playoffs, in particular - players on teams that go further or play in 7-game series will accumulate more because they have more opportunities.)

Some Minor Changes to the Equation

Please note that we've also updated the methodology, such that some players will have a slight variation in the BPM and associated stats. These were technical fixes to the regression methodology, which had the result of slightly changing the relative value of component stats. For example, blocks and shooting efficiency are two factors that are more highly favored by the revision and thus Anthony Davis saw the largest increase in BPM (+0.8), however most changes were of a much smaller magnitude. Please see the details of this revision in the write-up, under the "Updates" section.

Again, Basketball Reference extends its thanks to Daniel Myers, whose research the above represents. Also, please see the revised 'About BPM' write-up that details the methodology and is generally extremely useful for understanding the context of BPM and VORP, and the best ways to think about and use these stats.

## Using our Search Engine

23rd January 2015

When we revamped our search engine last year we didn't provide much instruction. After all, it's pretty simple to use. It's fast, features auto-complete, and has nicely categorized search results.

Since then, we've added some new features that should make finding what you want even easier. The following is a quick guide to the most useful tips and tricks.

First thing is first, the search bar is at the top right of the site, and also on the left-hand side of the homepage, shown here, respectively:

Player Search

We match against the player's common name or a known nickname: 'lebron' will return LeBron James; searching 'sir charles' will return Charles Barkley.

Partial strings work, too. For example, 'kentav' will return Kentavious Caldwell-Pope, if you want to save yourself some typing and the player's name is unique.

Team Names

Searching for team indexes and seasons is just as easy. 'spurs' will return all Spurs teams since they adopted that name for the 1974 ABA season.

Clicking on the right column - 'Team Seasons' - will give you a list of individual Spurs seasons, which bring you conveniently to a season summary page.

Team Seasons

In fact, there's an even easier way to get to a team's season page. Just add a year before or after the team name.

For example, '1996 bulls' or 'bulls 1996' will bring you directly to that champion Bulls season.

League Seasons

What if you want to get to a particular NBA season page to view historical standings, stats, and leaders?

Same trick as for teams, except use the league name: 'nba 1998' or '1998 nba'. This will land you on the 1998 NBA season summary. This pattern works for the ABA and BAA seasons, as well.

Playoffs

Likewise, to access historical playoff pages do the same thing, except substitute the word 'playoffs'.

'playoffs 1990' or '1990 playoffs' will send you to the 1990 Playoffs summary page, with links to series stats, leaders, etc.

Finals

Finals summaries work the same way.

'finals 1984' or '1984 finals' will give you all the Bird & Magic stats from that year's Finals.

et cetera

We get a lot of searches that don't fit a particular pattern - for example, mis-spellings like 'dwayne wade', or searches like 'hall of fame'.

Often, these will give you what you're looking for and the best way to find out is trial and error. In fact, 'dwayne wade' will go to Wade's page and 'hall of fame' will land you on our Hall of Fame summary page.

Likewise, 'mj' will bring you to Jordan's page, 'sixers' to the 76ers franchise summary, and 'salaries' will direct you to our database of player salaries.

If a common search is missing or there's a term or search pattern you'd like us to add here, please ask!

## Small Additions to the Player Season Finder

6th January 2015

Just a note that we've added 3-Point Attempt Rate (3PAr) and Free Throw Attempt Rate (FTr) to our Player Season Finder.

In addition, we've expanded the group of shooting stats that we show by default, now including both eFG% and TS%.

## Draft Stashes List and Stats

17th December 2014

If you've poked around our Draft section recently, you might have a noticed a new link for 'Draft Rights'. We've compiled a list of all held draft rights for players that are currently playing abroad.

The easiest way to view this is to mouse over the 'draft' item in the navigation bar and look for the link:

The selections are sorted by the retaining team, then by the year of selection. We have current year stats for all players that participate in one of the Liga ACB (Spain), LNB Pro A (France), Lega Serie A (Italy), or Greek Basket League, as well as the Euroleague or Eurocup. In these cases, the Current Team column will link to those team's pages and you can view the player's season stats there.

Finally, if that's not enough, on our team pages we've included the current year stats for all players whose draft rights are retained by that team. In some cases, the player will play in a league for which we don't have stats or might not currently be under contract with a team, but most players whose rights are currently held are active and playing in Europe...

24th November 2014

Users of our Play Index have likely grown accustomed to searching through the Team Game Finder to find things like highest-scoring games or best shooting performances. However, over the years basketball fans (and our users) have grown more statistically savvy and often crave a deeper perspective beyond the raw numbers. For that reason, we have included an advanced box score within our games boxes for some time. Now, we have taken the next step by allowing users to search through these advanced statistics via the Team Game Finder.

To use these tools, you can simply go to the link above and set the parameters you would like for your search. Please note that these advanced stat searches are limited to the era for which we have complete box scores (since 1985-86). Here are some examples:

Please note that cumulative searches utilizing possession-based metrics will differ slightly from some season totals found on team pages and in the team season finder because our box scores have player turnovers, but not team turnovers, which causes slight variations.

## Player Season Finder Improvements, Including BPM & VORP

13th November 2014

Just a note that we've expanded the searchable options in our Player Season Finder this week.

In particular, we've added BPM and VORP to the list of searchable stats, both of which are available going back to the 1973-74 season.  If you don't know what those stats are, you may have missed this recent announcement. Also feel free to weigh in at the discussion on the APBRmetrics forum.

Also, we've added search options by a player's birth state, college, and debut seasons, either in the NBA or ABA. There's also a new option to search by award winners so you can see all seasons by MVP winners, All-NBA selections, Defensive Players of the Year, etc.

If you're new to the site, the Player Season Finder is our most popular database search tool. You can get to it by clicking on 'play-index' in the top navigation menu, then the large 'Player Season Finder' link. It allows you to search for and compare player stats for a season or a player's career (or a span of years). You can also find the number of seasons that match your criteria. As an example, you can find the highest USG% seasons of all timemost career VORP for a player from Duke, or the most points scored in a single postseason.

The new fields are highlighted in red below: