Bayeselo

Bayeselo, or Bayesian Elo Rating, is a modifier form of ELO used to calculate the ratings on the Seasonal Ladder.

See Bayesian Elo Rating for the full details. This has several advantages over other ELO rating systems:

• Beating the same opponent multiple times gives you more rating than beating them once. In most ELO systems, only a win or loss is considered for each opponent.
• Bayeselo behaves correctly when opponents' ratings are far apart
• Ratings are calculated based on final ratings, not just what the rating was when the game took place.

The exact algorithm used by this tool is documented on their page, and is not repeated here. The source code is also available for the truly nerdy.

Run your own Ladder Simulations

You can run your own ladder simulations which help to understand how the ratings are calculated. This can be used to answer questions like:

• How would the ratings be different if I had won versus X instead of lost?
• How would the ratings change if I win or lose this in-progress game?
• How would the ratings be different if first-pick advantage was higher or lower?

Here’s the process to re-produce the current rankings:

• Download Bayeselo.exe from remi.coulom.free.fr.
• Download BayeseloLog.txt from the links below. This file is automatically generated each time the ladder updates and contains all of the commands needed to re-produce the current ladder rankings.
• Run Bayeselo.exe. You’ll be left at a prompt that says

ResultSet>

• Get BayeseloLog text file:
  • Visit this page to get the list of seasons
  • Click the season you want the log for
  • Check your URL, and you'll see it ends with ID= and a number. For example, Season XXX is ID=4029
  • Enter that number into this URL: http://data.warlight.net/Data/BayeseloLog4029.txt

• Copy the entire contents of BayeseloLog.txt to your clipboard, and paste it into the Bayeselo application. (Note: To paste into a console app on windows, you can right-click on the titlebar, select Edit then Paste)

This will produce rankings like the following:

Rank Name                      Elo    +    - games score oppo. draws
   1 Waya                      303  457  341     1  100%   179    0%
   2 Fizzer                    302  412  285     2  100%   115    0%
   3 Soyrice                   218  297  240     2  100%    87    0%
   4 FBGDragons                181  494  353     1  100%    52    0%
   5 NoZone                    179  219  235     3   33%   220    0%
   6 FBGMoDogg                 110  326  421     1    0%   218    0%
   7 Ruthless                   83  410  281     2  100%   -99    0%
   8 GuyMannington              65  311  312     2   50%    45    0%
   9 deweylikedonuts            55  304  304     2   50%    59    0%
  10 Perrin3088                 52  222  217     5   60%   -45    0%
  11 sue                        50  457  340     1  100%   -69    0%
 ...

Making changes

Now that you can re-produce the existing ladder rankings, you can try making changes and seeing how they affect the results. Here’s the process:

• First, ensure you are on the “ResultSet>” prompt. If you’re in “ResultSet-EloRating>”, enter a command of just “x” to go back up one.
• Enter the command “reset” to clear the previous results. This ensures you’re starting from a clean slate.
• Modify BayeseloLog.txt depending on what you want to try (see below).
• Copy/paste the modified BayeseloLog.txt back into Bayeselo.exe to see the results. Compare to your previous run to see how they changed.

Modifying the log

In BayeseloLog.txt, you’ll find two large sections – first, a bunch of addplayer commands, then a bunch of addresult commands.

Players

Each addplayer line corresponds to a player participating (or that has participated at one time) in the ladder. They are also numbered, starting at zero and going up.

addplayer Fizzer ;0
addplayer Knoebber ;1
addplayer FBGDragons ;2
addplayer CuChulainn ;3
...
addplayer Perrin3088 ;7
...

Results

After the players, there are a bunch of addresult commands. Each addresult corresponds to one finished ladder game. In these numbers, we tell Bayeselo which two players fought each other, who got first pick, and who won. Let's examine this in detail.

addresult 0 7 2
addresult 1 4 2
addresult 2 7 2
addresult 3 7 0
addresult 4 18 0
...

By changing these, you can simulate new wins/losses or change existing games to see how they would affect the results.

See Also

• Ladders