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First 2012-13 Update Likely to be Delayed

Posted by Justin Kubatko on October 30, 2012

Due to storm damage at our data provider's ISP, it is unlikely that Basketball-Reference.com will be updated tomorrow morning with the results from opening night. We will try to get these results up as soon as possible. Our apologies for the inconvenience.

Update: It turns out the update was not delayed. The site should now be updated with the results from last night. Please let us know if you find any bugs.

Comments Off | Posted in Announcement, Basketball-Reference.com, expire2d

Estimating NFL Win Probabilities for Matchups Between Teams of Various Records

Posted by Neil on October 30, 2012

WARNING: Math post.

PFR user Brad emailed over the weekend with an interesting question:

"Wondering if you've ever tracked or how it would be possible to find records vs. records statistics....for instance a 3-4 team vs. a 5-2 team...which record wins how often? but for every record matchup in every week."

That's a cool concept, and one that I could answer historically with a query when I get the time. But in the meantime, here's what I believe is a valid way to estimate that probability...

  1. Add eleven games of .500 ball to the team's current record (at any point in the season). So if a team is 3-4, their "true" wpct talent is (3 + 5.5) / (7 + 11) = .472. If their opponent is 5-2, it would be (5 + 5.5) / (7 + 11) = .583.
  2. Use the following equation to estimate the probability of Team A beating Team B at a neutral site:

    p(Team A Win) = Team A true_win% *(1 - Team B true_win%)/(Team A true_win% * (1 - Team B true_win%) + (1 - Team A true_win%) * Team B true_win%)

  3. You can even factor in home-field advantage like so:

    p(Team A Win) = ((Team A true_win%) * (1 - Team B true_win%) * HFA)/((Team A true_win%) * (1 - Team B true_win%) * HFA +(1 - Team A true_win%) * (Team B true_win%) * (1 - HFA))

    In the NFL, home teams win roughly 57% of the time, so HFA = 0.57.

This means in Brad's hypothetical matchup of a 5-2 team vs. a 3-4 team, we would expect the 5-2 team to win .583 *(1 - .472)/(.583 * (1 - .472) + (1 - .583) * .472) = 61% of the time at a neutral site.

Really Technical Stuff:

Now, you may be wondering where I came up with the "add 11 games of .500 ball" part. That comes from this Tangotiger post about true talent levels for sports leagues.

Since the NFL expanded to 32 teams in 2002, the yearly standard deviation of team winning percentage is, on average, 0.195. This means var(observed) = 0.195^2 = 0.038. The random standard deviation of NFL records in a 16-game season would be sqrt(0.5*0.5/16) = 0.125, meaning var(random) = 0.125^2 = 0.016.

var(true) = var(observed) - var(random), so in this case var(true) = 0.038 - 0.016 = 0.022. The square root of 0.022 is 0.15, so 0.15 is stdev(true), the standard deviation of true winning percentage talent in the current NFL.

Armed with that number, we can calculate the number of games a season would need to contain in order for var(true) to equal var(random) using:

0.25/stdev(true)^2

In the NFL, that number is 11 (more accurately, it's 11.1583, but it's easier to just use 11). So when you want to regress an NFL team's W-L record to the mean, at any point during the season, take eleven games of .500 ball (5.5-5.5), and add them to the actual record. This will give you the best estimate of the team's "true" winning percentage talent going forward.

That's why you use the "true" wpct number to plug into Bill James' log5 formula (see step 2 above), instead of the teams' actual winning percentages. Even a 16-0 team doesn't have a 100% probability of winning going forward -- instead, their expected true wpct talent is something like (16 + 5.5) / (16 + 11) = .796.

(For more info, see this post, and for a proof of this method, read what Phil Birnbaum wrote in 2011.)

3 Comments | Posted in Announcement, Pro-Football-Reference.com, Stat Questions

Incomplete Stats for 10/29

Posted by Mike on October 30, 2012

Due to hurricane-related issues with our data provider, stats for the Monday night NFL game are incomplete. We will update them as soon as we have the data, but until that point the player pages for 49ers and Cardinals players will be missing yesterday's game stats.

Comments Off | Posted in Announcement, expire7d, Pro-Football-Reference.com

Support Pro-Football-Reference.com, Sponsor a Page

Posted by Neil on October 29, 2012

Sponsoring a page is fun, fast, and easy way to support what we're doing here at Pro-Football-Reference. With a sponsorship, you can:

  • Show your support for your favorite player or team.
  • Drum up traffic for your own site & draw in fans with a common interest.
  • Get some well-deserved recognition for your support of PFR.
  • Make your voice heard by the tens of thousands of people who visit Pro-Football-Reference every day.

Here's all you have to do to get involved:

  1. Create a membership account.
  2. Find the page(s) you'd like to support, and click "sponsor" (available pages).
  3. If the page you want is already sponsored, click "Alert Me!" to be informed when the current sponsorship expires.
  4. Follow the instructions to create your message and make your payment.
  5. Your message and links will be visible on the page after we approve them (usually in less than 24 hours).

And who knows, if you're clever enough, your message might end up on lists like these.

Comments Off | Posted in Announcement, Pro-Football-Reference.com, Sponsors

PI Player Game Finder

Posted by Neil on October 28, 2012

Comments Off | Posted in Announcement, Play Index, Pro-Football-Reference.com

PI School Game Finder

Posted by Neil on October 27, 2012

Comments Off | Posted in Announcement, CFB at Sports Reference, Play Index

1992 United States Select Team Roster

Posted by Neil on October 26, 2012

With the Dream Team documentary and book coming out this summer, I've gotten asked several times to provide the roster for the '92 U.S. Select Team that famously defeated the Dream Team before they went to Barcelona for the Olympics. For posterity, here was the roster of that team, which was made up of the top college players of the day:

1992 United States Development Team

Head Coach: George Raveling (University of Southern California)
Assistant Coach: Roy Williams (University of Kansas)
Athletic Trainer: Ron Linfonte (St. John's-NY)
Manager: Dennis Johnson (University of Southern California)

Roster

NBA Career Stats
Player (ncaa stats) Ht Wt Age DOB College G PPG TS% RPG APG S+B/G PER WS48 p(HoF)
Anfernee Hardaway (ncaa) 6-7 195 20 7/18/1971 Memphis 704 15.2 53.5 4.5 5.0 2.0 17.4 0.125 4.8%
Grant Hill (ncaa) 6-8 225 19 10/5/1972 Duke 997 17.1 55.2 6.1 4.2 1.8 19.2 0.140 40.7%
Allan Houston (ncaa) 6-6 200 21 4/20/1971 Tennessee 839 17.3 54.6 2.9 2.4 0.8 14.9 0.094 0.9%
Bobby Hurley (ncaa) 6-0 165 20 6/28/1971 Duke 269 3.8 44.3 1.1 3.3 0.5 8.1 -0.014 0.0%
Jamal Mashburn (ncaa) 6-8 240 19 11/29/1972 Kentucky 611 19.1 50.4 5.4 4.0 1.2 15.7 0.092 2.9%
Eric Montross (ncaa) 7-0 270 20 9/23/1971 UNC 465 4.5 49.7 4.6 0.4 0.9 9.1 0.048 0.0%
Rodney Rogers (ncaa) 6-7 235 21 6/20/1971 Wake 866 10.9 52.7 4.5 2.0 1.5 14.4 0.085 0.0%
Chris Webber (ncaa) 6-9 245 19 3/1/1973 Michigan 831 20.7 51.3 9.8 4.2 2.9 20.9 0.132 74.6%

(Source: USA Basketball)

2 Comments | Posted in Announcement, Basketball-Reference.com, CBB at Sports Reference, History

How To “SHARE” B-R Stats

Posted by Neil on October 22, 2012

If you've spent a lot of time at Baseball-Reference, you've probably seen the "SHARE" command in red text above a table of stats... but maybe you don't know what that does, or have forgotten how to use it. No worries -- here's a quick rundown of the features you can access by clicking "SHARE":

  • Customize rows & columns - Sharing lets you delete certain rows/columns that you don't want to include in your table. Just click the round 'x' button to delete a specific row/column, or the arrow 'x' to get rid of everything to the right (columns) or directly below (rows) the row/column in question.
  • Export as an HTML table - Clicking 'html
    ' gives you code to embed the table onto your site (you can even choose to keep S-R's inline style formatting).
  • Get a link - Choosing Link URL creates an SR tiny URL specifically for the table you created, which can easily be sent to others via twitter or directly linked at your blog.
  • Export as bbcode - This option lets you copy-and-paste the table into most bulletin board formats.
  • Export into a javascript widget - This will give you code to embed the static table on your site via a js widget. (Note: The 'Embed' option next to 'SHARE' allows you to do this as well, but as a constantly-updated table instead of a static one.)
  • Export as an iframe - For those who prefer to embed the table within an inline frame.
  • Export into preformatted text or CSV
  • Convert table to Wiki formatting - This will turn the table into a format suitable for sites like Wikipedia.

Happy sharing!

Comments Off | Posted in Announcement, Baseball-Reference.com, HowTo

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