Swiss System

From DipWiki

A Swiss System tournament is a commonly used type of tournament in Chess, Bridge, Scrabble, Squash and other games where players or teams need to be paired to face each other. This type of tournament was first used in a Zurich chess tournament in 1895, hence the name "Swiss System".

Used primarily for tournaments where the Players-per-board is typically only 2 (one person vs one person) the system has been extended to apply to Diplomacy for the Winter Blitz.

The Pairing Procedure

The principle of a Swiss tournament is that each player will be pitted against other players who have done as well (or as poorly) as him or herself.

The first round is seeded according to rating. Players will receive points based on the result of their game. Win, lose, or draw, all players proceed to the next round where winners are pitted against winners, losers are pitted against losers, and so on. In subsequent rounds, players face opponents with the same (or as close as possible) score. No player is paired up against the same opponent twice.

The Basic Rules:

First round:

Players are ranked according to rating, then alpha. Then the list of players is divided into groups based on the number of players per board. For a typical Diplomacy tournament this is 7. The top 7 players make group A, the next 7 group B, etc to the last 7 making group G. Then The 1st player from each group is assigned to the first game board. The 2nd player from each group assigned to the 2nd board, etc.

This ensures a theoretical diversity of players on every board.

Subsequent rounds:

Players are ranked according to score first, then rating, then alpha. The list of players is then cut in half. (If 9 or more boards are played, players may be broken into thirds) If there were an even number of boards in round 1, then the division is exactly half. If there were an odd number of boards, then either 3 players are "pulled up" or "pushed down" to create the most logical score break.

Then within those two subsets of players (the "winners" and the "losers") the players are ranked according to score, rating, alpha, and paired up per the first round method.

Modifications are made to prevent players from meeting each other twice.

The Implications

Determining a clear winner typically requires the same number of rounds as an Elimination tournament, that is a tournament with X players-per-board and Y rounds can handle X to the Y players:

  • In a 2-player game, one round can handle 2 players, 2 rounds can handle 4 players, etc.
  • In 7-player Diplomacy, one round can handle 7 players, 2 rounds 49 players, etc.

This will not always produce a perfect result:

  • It is not uncommon to have more players than the perfect number, and if fewer than the ideal number of rounds are played, it can happen that two or more players finish the tournament with a perfect score, having won all their games but never faced each other.
  • It is also not uncommon to have games end without a definite solo winner, leading to lower overall scores and a higher probability of ties.

Compared to an Elimination tournament, the Swiss System has the inherent advantage of not eliminating anyone. That means that a player can enter such a tournament knowing that he will be able to play in all rounds, regardless of how well he does.

Another advantage compared to Elimination tournaments is that the final ranking gives some indication of relative strength for all contestants, not just for the winner of the tournament. As an example, the losing finalist in an Elimination tournament may not be the second best contestant; that might have been any of the contestants eliminated by the eventual tournament winner in earlier rounds. In the Swiss System, those who lose early on should be able to prove their relative strength against the lower competition they'd be paired with in subsequent rounds for an overall good score. One could argue that it is a strategy in lieu of a win, to try to place "just below half" so as to be the highest player in the lower half going into the 2nd round to be paired up against the lower half.

Compared with a Round Robin tournament, a Swiss System can handle many players without requiring an impractical number of rounds. An Elimination tournament is better suited to a situation in which only a limited number of games may be played at once. In a Swiss system, all players can be playing a round at the same time.

Written by: Michael Sims, Diplomaticcorp. mike-at-diplomaticcorp-dot-com Feel free to contact me for any suggestions, clarifications, or corrections.

See also: Pairing Systems