Duplicate bridge is the most widely used variation of contract bridge in club and tournament settings. It is called duplicate because the same bridge hand (i.e. arrangement of cards) is duplicated at other tables, in order to allow a fair comparison of playing skill and reduce "luck of the cards". In this way, every hand, whether good or bad, is played in competition with others playing the identical cards, and the element of skill is heightened whilst that of chance is reduced. Duplicate bridge stands in contrast to rubber bridge where each hand is freshly dealt and scores depend as much on the cards as on the players.
Bridge boards, simple four-way card holders, are used to enable each player's hand to be passed intact to the next table that must play the deal, and final scores are calculated by comparing each pair's result with others who played the same hand. Bidding boxes are often used to facilitate the mechanics of bidding, prevent inadvertent passing of information, and minimize the noise level.
In duplicate bridge, a player normally plays with the same partner throughout an event. The two are known as a "pair". There are two exceptions: on team events with five or six members swapping partners for portions of the event, and in individual tournaments, in which players change partners for each round.
The tournament consists of rounds, which present a number of boards, usually two to five, to be played against the same opponents. After a round, some or all of the players reseat themselves according to a prescribed movement, so that each pair opposes a different pair in each round; the boards are also moved. The movement must be set up so that every pair does not play more than one round against same opponents, and, of course, does not play the same board not more than once. The tournament director will select the movement in order to allow the given number of players to play the desired number of boards each, without repetition. A session typically consists of between 24 and 28 boards in total, but this can vary. If there are an odd number of pairs, one pair will have to sit out in each round. Most games are single-session, but tournament events can consist of two, four or more sessions.
The Howell movement is sometimes used instead, usually when there are a relatively small number of tables. The actual movement is more complicated and varies according to the total number of pairs. All boards and most pairs move after every round according to guide cards placed on the tables, or carried by the players (usually one pair, or sometimes more, remain stationary). The Howell is sometimes considered a fairer test than the Mitchell, because each pair faces all or nearly all of the other pairs, not just the pairs sitting in the opposite direction. However the fairness of a movement depends not only on who one plays against but also to a considerable extent on one's indirect opponents, ie those who play the same cards as you do. The Howell also tends to be more error-prone than the Mitchell due to its greater complexity.
Less common is the Chalfant movement. In this movement, the boards remain stationary while the players move according to guide cards. This requires significantly more physical tables, because several tables are not in play on any given round. (Like the Howell movement, this movement is typically used when there is a relatively small number of players, typically no more than 12 pairs. Also like the Howell movement, this movement produces a single winner and pairs face all or almost all of the other pairs in play.) This movement has the advantage that pairs are often moving to a table that was not in use on a previous round, so a slow pair does not delay as many other pairs as in a Howell. Also, for several sizes, this movement is technically superior in that more pairs face all other pairs than in the corresponding Howell movement. This movement has the disadvantage of requiring a larger number of physical tables, and thus more space. It also requires the players to carry guide cards with them and consult them, while the guide cards usually remain on the tables for Howell movements.
Whatever movement is used, if the number of pairs is odd, obviously one pair must sit idle during each round; that situation is referred to as a bye or sit out. In that undesirable case, the missing pair (sometimes called the phantom pair) is treated as if it exists, i.e. the movement is set up for (number of actual pairs + 1)/2 tables. The phantom pair may be North-South, East-West or an arbitrary pair number in a Howell movement. In a Mitchell movement, having an East-West phantom pair is advantageous in that there are non-phantom players at each table responsible for correct movement of the boards. During the movement, one pair in each round will sit out ("play" against the phantom pair). Since, as result, pairs will usually play unequal numbers of boards, their final results are normally scaled in the final calculation (known as factoring), or less commonly they might be awarded "bye points" for that round (normally, a result slightly above average).
Another arrangement for an odd number of pairs is called a bump movement, in which the number of tables is rounded down to (number of actual pairs - 1)/2. Normally, the extra pair sits out the first round and then, according to a schedule, substitutes for a different North-South pair for each subsequent round (the "bumped" pair having a sit out for that round). In particular, the bump is preferable to the sit out for 11½ tables: it allows every pair to play at least 24 boards while having only 33 boards in play.
Trials are usually reserved for high-level competitions (such as regional and national championships, invitation tournaments etc.). There, a fixed number of pairs (usually 16) play a full round-robin tournament (Swiss can be also used to shorten the tournament) with relatively long matches (8-32 boards) against each other, the entire tournament lasting for two to four days. One session consists of only one round, with boards circulating among the tables and pairs remaining seated. Results are calculated after each round using IMP or Calcutta scoring, converted to Victory points, and added up to the running score. The pair with highest VP score becomes the winner.
Suppose Team A plays Team B. The first time a hand is played, one partnership from Team A takes the North-South cards and one partnership from Team B takes the East-West cards; when the hand is played again, it is played by the other two partnerships, but this time with Team A holding the East-West cards and Team B holding the North-South cards. Of course the teams may not discuss the deals between the two plays. Normally, each of the two tables deals and plays half of the scheduled boards at the beginning of the match, and they're exchanged in the halftime. After each deal has been played twice, the scores per deal are compared, and a score is given depending on the net total score from the two times the deal was played. For example, if one pair scores +620 on a deal, and their teammates score -600, then the team's net score on that deal is +20.
Those are the two commonly used methods; sometimes are also used:
Individual events are more complex to run, and require that the players get accustomed to new partners on a frequent basis. Also, the outcome depends more on luck than in other types of events, as a good player often cannot do much when paired with a bad player, especially if the deal is complex. For those reasons they are less popular and less common than pair or team events, but some players are very fond of them.
These matchpoints are added across all the hands that a pair plays to determine the winner. Scores are usually given as percentages of a theoretical maximum: 100 percent would mean that the partnership achieved the best score on every single hand. In practice, the results in 60 to 65 percent range are likely to win the tournament. In a Mitchell movement (see above) the overall scores are usually compared separately for North/South pairs and for East/West pairs, so that there is one winner in each group (unless arrow-switching has been applied - see above).
A Historical Note: At some time in the past there were games in which both North--South and East--West would be awarded the same matchpoint score. In such a game the low East--West Score would be the winner. Example: There is one North--South Pair with a score of +500 in a U.S. Twelve Top Game. Currently that North--South would score 12 matchpoints on that board and the East--West would score Zero.
In Board-a-match team game, the matchpoints are calculated using a similar principle. Since there are only two teams involved, the only possible results are 2 (won), 1 (tied) and 0 (lost) points per board.
The score that is being compared against can be obtained in the following ways:
|Point difference||IMPs||Point difference||IMPs||Point difference||IMPs|
|220||260||6||1100||1290||15||4000 or more||24|
A more subtle difference is in the bidding of partscore hands. In duplicate bridge, once a pair recognizes that they are playing for part score (less than a game), their objective is to win the auction with the minimum bid. In rubber bridge, it may occasionally be desirable to bid above this minimum as points below the line may be needed to complete a game.
Duplicate bridge also has the advantage of compensating for a run of bad luck. A pair that has had poor hands all night may still have the highest score for the evening – as long as they play those cards better than the other pairs with the same poor cards (however in such cases the pair will probably have had less opportunity to exercise skill and their result will be more heavily dependent on the skill displayed by their opponents).
|Zone||Organization||Area||Member Countries||Total Membership|
|1||European Bridge League (EBL)||Europe||47||387,684|
|2||American Contract Bridge League (ACBL)||North America||4||158,429|
|3||Confederacion Sudamericana de Bridge (CSB)||South America||9||3,700|
|4||Bridge Federation of Asia & the Middle East (BFAME)||Asia||11||11,980|
|5||Central American & Caribbean Bridge Federation (CAC)||Central America||24||1,811|
|6||Pacific Asia Bridge Federation (PABF)||Pacific Asia (Far East)||13||30,098|
|7||South Pacific Bridge Federation (SPBF)||Australia and Oceania||4||49,095|
|8||African Bridge Federation (ABF)||Africa||17||6,308|