## Bayesian Elo Rating

4 stars based on 64 reviews

Bayeselo is a freeware tool to estimate Elo ratings. It can read a file containing game records in PGN format, and produce a chessx 146-1 binary list. The example below shows how to compute ratings from a PGN file wbec. Chessx 146-1 binary you wish to get the output of the "ratings" command in a file, you may redirect its output like this: Bayeselo can also produce predictions for round-robin tournaments.

For instance, if wbec1to9. The EPoints column indicates the expected final score. ERank is the expected final rank. The matrix to the right indicates chessx 146-1 binary probability in percent for every player and every rank.

This prediction tool may also be applied to a running tournament, where some of the games have already been played. In order to do this, simply replace the addplayer commands in the script by.

In case the rating of one participant is unknown, you can set it manually with the elo command at the level of the prediction interface. The prediction tool also lets you change the number of points awarded for a win, a loss, and a draw.

This way, it can be applied to generate predictions chessx 146-1 binary the French Football Championship soccer in the USwhere a victory is 3 points, a draw 1 point and a loss 0 point. Default values are 1, 0. If you want more usage information, you can get a list of available commands with the? The fundamental formula of Elo theory gives the expected result E of a game as a function of the rating difference D of players.

The fundamental assumption of the Elo rating system is that the strength of a player can be described by a single value, and that game results are drawn according to the formula above. The problem of Elo evaluation consists in estimating the Elo rating of a chessx 146-1 binary of players, from the observation of results of their games. The fundamental Elo formula can be reversed to obtain an estimation of the rating difference between two players, as a function of the average score.

This is the chessx 146-1 binary of the Elostat approach, that works in two steps:. The main flaw of this approach is that the estimation of uncertainty does as if a player had played against one opponent, whose Elo is equal to the mean Elo of the opponents.

This assumption has bad consequences for the estimation of ratings and uncertainties:. Also, another problem is that the estimation of uncertainty in Elostat does as if the rating of opponents are their true ratings.

But those ratings also have some uncertainty that should be taken into consideration. All these problems of the Elostat approach can be solved using a Bayesian approach. The chessx 146-1 binary of the Bayesian approach consists in choosing a prior likelihood distribution over Elo ratings, and computing a posterior chessx 146-1 binary as a function of the observed results.

P Elos is the prior distribution. It will be chosen to be uniform in the rest of this discussion. In order to perform this calculation, it is necessary to assume a little more than the usual ELO formula. The expected score as a function of the Chessx 146-1 binary difference is not enough.

We need the probability of a win, a draw and a loss as a function of the Elo difference. The default values in the program were obtained by finding their maximum-likelihood chessx 146-1 binary over 29, games of Leo Dijksman's WBEC. A description of this algorithm is available in the Links section below.

In this section, I will present some facts that highlight the differences between the two programs, chessx 146-1 binary, I hope, should convince most readers that bayeselo is better than elostat. Still, I do not claim that bayeselo is perfect, chessx 146-1 binary criticism is welcome. Bayeselo has already benefited a lot from the feedback of its users, and I thank them for that.

If you find a situation where the output of bayeselo looks bad or strange, do not hesitate to let me know. In chess, playing with the white pieces is an advantage estimated to be worth about 33 Elo points. Bayeselo takes this into consideration.

For instance, after a single draw between two players A and B, A playing white, here are the outputs of elostat and bayeselo:. Note that the difference in estimated playing strength according to bayeselo is relatively small compared to the 33 Elo-point value of playing first.

That is because of a mechanism of bayeselo that requires many games to confirm a rating difference, detailed in the next subsection. After many such draws, bayeselo's estimated rating difference would be 33 points. Bayeselo uses a prior chessx 146-1 binary over ratings, that increases the likelihood that the ratings of players are close to each other. The consequence is that a high rating difference has to be deserved, and requires many more games than with Elostat.

A big source of problems in elostat is that it assumes that many games against many opponents is equivalent to as many games against one opponent whose rating in the average of ratings. This is very wrong, and fails badly in situations where opponent's ratings are far apart. Note that elostat gives a point difference between B and C. This is really completely wrong since the only information we have about chessx 146-1 binary relative strength is that B drew C. So their ratings should be close.

Bayeselo gives a small advantage to C, because it drew B while playing as black. This is probably the most severe weakness of elostat. It does not only show with that kind of artificial situation, but also in real tournaments. These ratings show big differences between bayeselo and elostat. These 4 players all participated in the "Promo D" tournament between chessx 146-1 binary and chessx 146-1 binary divisions. Natwarlal, Alarm, and NagaSkaki come from division 4.

NullMover from division 3. Results of the promotion tournament indicate that NullMover is weaker than Natwarlal NullMover scored So the ratings of bayeselo look OK according to the results of the promotion tournament, whereas those of elostat are completely wrong.