Editing Swiss-system tournament (section)

==Pairing procedure==
During all but the first round, competitors are paired based on approximately how they have performed so far. In the first round, competitors are paired either randomly or according to some pattern that has been found to serve a given game or sport well. If it is desired for top-ranked participants to meet in the last rounds, the pattern must start them in different brackets, just the same as is done in seeding of pre-ranked players for a single elimination tournament. In subsequent rounds, competitors are sorted according to their cumulative scores and are assigned opponents with the same or similar score up to that point. The pairing rules have to be quite complicated, as they have to ensure that no two players ever oppose each other twice, and to avoid giving a player some advantage as a result of chance.

The detailed pairing rules are different in different variations of the Swiss system. As they are quite complicated, and it is undesirable to have a long delay between rounds to decide the pairings, the tournament organizer often uses a computer program to do the pairing.

In chess, a specific pairing rule, called "Dutch system" by [[FIDE]], is often implied when the term "Swiss" is used. The Monrad system for pairing is commonly used in chess in Denmark and Norway, as well as in other sports worldwide. These two systems are outlined below.

===Dutch system===
The players are divided into groups based on their [[Elo rating system|scores]]. Within each group with the same or similar score, players are ranked based on ratings or some other criteria. Subject to the other pairing rules, the top half is then paired with the bottom half. For instance, if there are eight players in a score group, number 1 is paired with number 5, number 2 is paired with number 6 and so on. Modifications are then made to prevent competitors from meeting each other twice, and to balance colors (in chess).<ref name="scichess.org">{{cite web|url= http://scichess.org/faq/swiss.html |url-status=dead |archive-url= https://web.archive.org/web/20131118215711/http://scichess.org:80/faq/swiss.html |access-date=9 December 2013 |archive-date=18 November 2013 |title=Swiss System vs Round Robin |work=SciChess.org}}</ref> For this method to work, the score groups cannot be too small, and thus for smaller overall fields score groups are not a suitable approach.

This pairing system may have some issues with competitive integrity if a tournament where this system is used has qualifiers leading to it. For example, suppose a certain qualifier determines the 5th-8th seeds in an 8-team Swiss-style tournament. If the Dutch system is used, players or teams in the qualifier may be incentivized to not do their best, as doing so might make them play against the 1st seed on the first round, decreasing their chances of having a good score. Conversely, for knockout tournaments, the highest seed is usually paired with the lowest, the 2nd highest with the 2nd lowest, and so on. This incentivizes players or teams to do their best and get a higher seed so that they can play against lower-seeded players/teams.

===Monrad system===
The players are first ranked based on their scores, then on their starting numbers (which can be random or based on seeding). Then #1 meets #2, #3 meets #4, etc., with modifications made to ensure that other rules are adhered to. Players are sorted by scores (not score groups) and original ranks, then each player paired to the next opponent, typically excluding repeats.

The Monrad system used in chess in Denmark is quite simple, with players initially ranked at random, and pairings modified only to avoid players meeting each other twice.<ref>[http://www.dsu.dk/dsu-dok/skakhand/2007/sh4-14-2.pdf Regulations for Monrad system as used in Denmark] {{webarchive |url= https://web.archive.org/web/20070927232519/http://www.dsu.dk/dsu-dok/skakhand/2007/sh4-14-2.pdf |date=27 September 2007}} (See section 4.10.1) {{in lang|da}}</ref> The Norwegian system has an optional seeding system for the first-round pairings, and within a score group, the pairing algorithm endeavors to give players alternating colors.<ref>[http://www.sjakk.no/nsf/monradsystem_index.html Regulations for Monrad system as used in Norway] {{webarchive|url= https://web.archive.org/web/20070706122207/http://www.sjakk.no/nsf/monradsystem_index.html |date=6 July 2007 |lang=no}}</ref>