Movement is a term used in duplicate bridge events to describe how the players, tables and boards are arranged.
The aim of movement is to make the comparison between players as fair as possible. The minimum requirement of a movement is that a player must not play the same board twice, and in a team match, the opposing pairs of each team must play the same board.
In order to make the comparison as fair as possible, each board should be played by the same number of players, and the movement should be made in a way that each other player should contribute the same weight to a player's result.
A movement is said to be complete if everyone has played with all other opponents or all boards available in the movement provided.
Weighting of players[]
As the aim of a movement is to made the comparison as fair as possible, if the weights of different players are not the same, a particularly strong or weak player may affect different players differently.
The competition between two pairs in a pairs match can be calculated as follows, where n is the number of comparisons (the maximum number of MP in a MP match):[1]
- If they are direct opponents, n, because there are n matchpoints at stake;
- If they are indirect opponents (playing the same board in the same direction at different tables), 1, because 1 matchpoint is won or lost in comparison
- If they are indirect partners (playing the same board in the different direction at different tables), -1, because in different direction, a good result by the other player actually helps.
Similarly, in an individual match:
- If they are direct opponents, n;
- If they are direct partners, -n;
- If they are indirect opponents, 1;
- If they are indirect partners, -1.
For example, in a complete two-winner Mitchell movement with n tables, the competition between any NS and EW pairs is exactly 0, therefore effectively they are separate fields, and it's totally appropriate to produce 2 ranking lists, while the competition between any 2 NS pairs, or any 2 EW pairs, is n-1.
In a perfect one-winner pairs movement, each pair plays against each other pair once, and when not in direct competition, half of the time in the same direction and half of the time in the direction, eliminating the indirect competition between pairs.
Similarly, in a perfect one-winner individual movement, each individual plays with each other at LHO, partner, and RHO once, and when not in direct competition, divided equally at LHO, partner, and RHO as well.
Overview of pairs movement[]
n refers to the number of complete tables. A board group consists of a fixed number of sequential boards to be played in a round, for example, if a board group consists of 4 boards, the groups are 1-4, 5-8, 9-12, etc.
| Name | Winners | Number of rounds | Number of board groups in play | Number of board groups played | Number of times a board is played | stationary pairs | sharing required |
|---|---|---|---|---|---|---|---|
| Mitchell (odd number of tables) |
NS & EW | n | n | n | n | All N/S pairs | No |
| skip Mitchell (even number of tables) |
NS & EW | n - 1 | n | n - 1 | n - 1 | All N/S pairs | No |
| relay Mitchell (even number of tables) |
NS & EW | n | n | n | n | All N/S pairs | Yes |
| Mitchell with phantom pair (even number of complete tables) |
NS & EW | n+1 | n+1 | n by NS, n+1 by EW | n | All N/S pairs | No |
| Mitchell with rover (odd number of complete tables) |
NS & EW | n | n | n-1 by NS (except the highest numbered fixed pair), n by EW | n | All N/S pairs except the rover, except when displaced | No |
| Howell | one winner | 2n - 1 | 2n - 1 | 2n - 1 | 2n | 1 pair only | No (except 2 or 3 tables only) |
Choosing a movement[]
As there isn't a "right" movement, tournament directors choose a movement based on practical considerations, which may include:
- The length of session (for example, if 25 boards are desired, with 6 pairs, a complete 3-table Howell movement is desirable, playing 5 boards each round; however, with 8 pairs, a complete Howell movement either produces 21 boards with 3 boards per round, or 28 boards with 4 boards per round)
- The field size (Howell movement is ideal for a small number of tables, but if there are too many tables, it becomes impractical)
- If extra physical boards and board duplicating machines are available (Some movements require sharing of boards, sometimes with distant tables. If there are many tables sharing boards, it is only practical if copies can be provided)
- If extra participants can be added with a short notice (e.g. a Mitchell movement can easily accommodate extra pairs by putting an extra table, but a Howell movement needs replacement of all table cards).
- If disability of participants require more stationary pairs.
- If the tournament needs to be curtailed when time runs short.
- If stronger or weaker players need to be placed in strategic positions.