Keywords: Tournament

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SODOS (or SDOS) stands for Sum Of Defeated Opponents' Scores and is a tie-breaking method sometimes used in round-robin tournaments. Chess players call it Sonneborn-Berger. Another name is [ext] Neustadtl score.

Its use as first tie breaking method in swiss tournaments is controversial. In practice it is only used after less disputed tiebreakers like SOS. SODOS is equivalent to "sum of defeated opponents' wins", when used properly.

In McMahon tournaments the tied players will not, in general, have the same number of wins, so several organizations advise against using SODOS in McMahon tournaments. It definitely should not be used, when negative initial McMahon scores are used in tournament. If SODOS is used in McMahon tournaments, it is sometimes called SODOMS (Sum Of Defeated Opponents McMahon Scores). Read more at /discussion).

As the name SODOS suggests, its value depends upon how many opponents you have defeated. If you lose all your games then your SODOS is zero. If you beat two others then it is the sum of two scores. If you beat 10 others then it is the sum of 10 scores. A draw against another player will see half their score added.

The intent behind using it is to discover how strong your opponents were. The theory is that if you have defeated a stronger set of opponents than another player on the same final score, then you are slightly stronger/better than they are.[1]

SODOS is used in round robin tournaments, because in round robin tournaments all players will have the same contributors to their SOS and SOSOS score.

Example in a round robin tournament

In a double Round Robin tournament each player has played two games against each other player. 1 indicates a win, 0 a loss.

     | 1st     | 2nd     | won games        | SODOS        |
     | round   | round   |                  |              |
     |---------+---------|                  |              |
     | A B C D | A B C D | wins  | opponent | wins         |
 | A | - 1 1 1 | - 0 1 0 |   4   | B C C D  | 4+3+3+1 = 11 |
 | B | 0 - 1 1 | 1 - 0 1 |   4   | A C D D  | 4+3+1+1 =  9 |
 | C | 0 0 - 1 | 0 1 - 1 |   3   | B D D    | 4+1+1   =  6 |
 | D | 0 0 0 - | 1 0 0 - |   1   | A        | 4       =  4 |

Player A and B both have 4 wins, because all players played each other Player A and Player B have the same SOS score. (16) Thus SODOS is used to determine the tournament winner: For each won game the opponent's final primary score is added to the winner's Sonneborn-Berger score. For example, A won against B, C, C and D, his Sonneborn-Berger score is 4+3+3+1 = 11. B has a Sonneborn-Berger score of 9, thus A is the tournament winner.


See also:

This page was WMEd by SGBailey on 2004-12-18. The entire old contents of the page was appended to the discussion page. Original input from me, Geoff Kaniuk, Matti, barry, Christopher Gerlach, Jens Baaran, DrStraw, wms.

SODOS last edited by on December 14, 2020 - 08:56
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