Duplicate bridge

Duplicate bridge tournament playing area

Duplicate bridge is the most widely used form of bridge used in tournament settings, and is also played in many bridge clubs. It is called "duplicate" because the same bridge hand is played multiple times, using boards to keep and pass each player's hand intact. Final scores are calculated by comparing your results with others who played the same hand.

The major organizations are:

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.

Game types

Pairs game

In a pairs game, each deal is played a number of times, after which all the scores are compared. Every score is written into traveling sheet, which travels with the board, containing at least numbers of N-S and E-W pair and the score. The more common form of overall scoring is matchpoint scoring, with IMP scoring second. Every pair plays against many opponents, depending on the size of the field. With common small tournaments with up to about dozen tables, every pair plays against cca. 50% of other pairs (Mitchell movement); with smaller number of tables, they may play with a higher percentage of pairs (Howell movement), and with larger fields the tournament can be split into separate sections (every section being a "sub-field", but the results being reckoned across entire field).

Each round consists of a number of boards, usually two or three, sometimes four or five. After a round, some or all of the players reseat themselves according to a prescribed movement, so that each partnership pair opposes a different pair for each round; the boards are also moved. A session normally consists of 24 to 28 total boards, but this can vary in special circumstances. Most games are a single session, but tournament events are sometimes two, four or more sessions.

The Mitchell movement is the most common. The North-South pairs remain stationary. After each round, the East-West pairs move to the next higher table and the boards move to the next lower table. In case of an even number of tables, the East-West pairs are told to skip a table after about half the rounds so that they do not encounter boards that they have already played; alternatively ("Relay Mitchell"), a "relay" (playerless table) is introduced at half of the field, while first and last table share the boards from the same round. The "perfect" Mitchell is seven or nine tables, with 4 or 3 boards per round respectively: all players play all boards, and all pairs of each direction play all pairs of the other direction.

The Howell movement is sometimes used instead, usually when there is a relatively small number of tables. The actual movement is more complicated and varies by the total number of pairs. All pairs and boards move after every round according to guide cards placed on the tables (but in some cases one or two pairs 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 the opposite direction.

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 typicaly 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 remain on the tables for Howell movements.

Team game

In a team game, two pairs normally constitute a team. (Teams of five or six members are often permitted, but only four members play at any given time.) Two teams compete using two tables and having one pair from each team seated at each table, at opposite directions. (For example, team A may sit North-South at table 1 and East-West at table 2; then team B would sit East-West at table 1 and North-South at table 2.) A relatively larger number of boards are played (usually six to eight for "Swiss teams", usually 12, 24, or more for knockout events). The boards are moved (usually by a caddy) so that they are all eventually played at both tables.

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. 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 +1000 on a deal, and their teammates score -980, then the team's net score on that deal is +20.

Several forms of scoring are then used to calculate the winner of the match. IMP scoring is most frequently used in team games, with Board-a-match (resembling matchpoint scoring) second.

At IMP scoring, the difference is converted using the IMPs table that "compresses" big differences in score. Often, the total difference in IMPs of a single match is converted into so-called Victory points, which are summed up to determine the overall team ranking.
At Board-a-match (BAM), each hand has equal weight; each hand is won, lost, or tied.

Those are the two commonly used methods; sometimes are also used:

Total point score uses no conversion whatsoever; total-point scoring was more popular in the past, and is applied mostly for events where only two teams play an extremely long match.
Patton scoring combines the methods of Board-a-match and Total point scoring.

Individual events

An individual event in duplicate bridge is one where each round a player is paired with a different partner. Scoring is usually using matchpoint pairs scoring, but IMP pairs scoring can be used. There are various methods for assigning partners. In some methods, a given set of players always sit North, another set sit South, another set sit East, and a final set always sit West. This can be used to ensure that each pair consists of a relatively experienced or skilled player, and a relatively inexperienced player.

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.

Scoring

Matchpoint scoring

The most common form of pairs game is the matchpoint pairs game. (See Bridge scoring for the scoring method of individual deals.) In the final calculation, each partnership scores 2 matchpoints for each other partnership that scored fewer points with the same cards, and 1 point for each partnership that scored the same number of points. Thus, every board is treated equally, with the best result earning 100% of matchpoints available for given board, and the worst with 0% matchpoints; the opponents receive the complement score, i.e. 80% result for N-S pair implies 20% for their E-W opponents. Colloquially, scoring the maximum number of matchpoints on a certain board is known as a "top board", and scoring zero matchpoints is a "bottom board". The terms "high board" and "low board" are also used.

Note 1: in the United States, scoring is 1 point for each pair beaten, and one half-point for each pair tied.

Note 2: The above rule of 2-versus-1 matchpoint is actually easy to apply in practical calculation. If the board is played n times, the top result achieves 2*n-2 matchpoints, the next 2*n-4, down to zero. When there are several identical results, they receive the average. However, complications occur when not every board is played equal number of times, or when an "adjusted" (director-awarded) score occurs. These cases can result in non-integer numbers of matchpoints ? see Neuberg formula.

These matchpoints are added to determine the winner. Scores are usually given as percentages of a theoretical maximum: 100% would mean that the partnership achieved the best score on every single hand. In practice, the results in 60-65% range are likely to win the tournament.

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.

IMP scoring

In IMP (International Match Points) scoring, every individual score is subtracted from another score, and the difference is converted to IMPs, using standard IMP table below. The purpose of the IMP table, which has sublinear dependency on differences, is to reduce results occurring from huge score differences ("swings").

The score that is being compared against can be obtained in the following ways:

In team events, it is the score from the other table;
In pair events, it can be:
- The datum score, most often calculated as the average score on board, excluding a number of top and bottom results. Sometimes, the median score is used instead.
- In "cross-imps" or "Calcutta" scoring, every score on board is compared against every other score (sometimes excluding top and bottom results) and IMPs summed up (and possibly averaged, to reduce "inflation").

IMP Table

Point difference		IMPs	Point difference		IMPs	Point difference		IMPs
from	to	IMPs	from	to	IMPs	from	to	IMPs
0	10	0	370	420	9	1750	1990	18
20	40	1	430	490	10	2000	2240	19
50	80	2	500	590	11	2250	2490	20
90	120	3	600	740	12	2500	2990	21
130	160	4	750	890	13	3000	3490	22
170	210	5	900	1090	14	3500	3990	23
220	260	6	1100	1290	15	4000 or more		24
270	310	7	1300	1490	16
320	360	8	1500	1740	17

Scoring and tactics

The type of scoring significantly affects pair's (team's) tactics. For example, at matchpoints, making one more overtrick than everybody else on a board gives the same result (the top) as making a slam that nobody else bid, whereas at IMP scoring, the difference comes down to 1 IMP (30 points) in the first case, but 11 or 13 IMPs (500 or 750 points) in the second case. In general, matchpoint scoring requires more "vivid" and risk-taking approach, while IMP scoring requires more careful and delicate handling (sometimes referred to as "cowardly" by ones who dislike it). The main features of the tactics are:

Matchpoints
- Overtricks are important
- Safety play is often neglected in the hunt for overtricks
- Thin games and slams are avoided
- Sacrifices are more frequent; e.g. going down 500 points doubled is worthy against opponents 620 points for a game.
- Doubles are more frequent, as they increase the score for the penalty.
- Playing in higher-scoring denominations (notrump or major suits) is important, as it may lead to an extra 10 or 20 points.
IMPs
- Overtricks are not important, as it's not worth the risk of losing e.g. game bonus (300-500 points = 8-11 IMPs) for potential 1-IMP gain for an overtrick
- Safety play is very important, for the same reason
- Thin games and slams are often bid. Bidding a game with 40% probability of success vulnerable and 45% nonvulnerable, with a small slam with 50% probability, constitutes an equal deal, and anything over that increases the possibility of positive IMP score in the long run.
- Sacrifices are less frequent, as they may be risky.
- Doubles are less frequent, as they may be risky. Often, when an opponents' contract is doubled, it turns declarer's attention to the bad lie of cards, and may induce him to take a successful line of play that he wouldn't take otherwise.

Contrast with rubber bridge

Duplicate bridge, especially matchpoint games, differs from rubber bridge: whereas the goal in rubber bridge is to win more points than the pair of people you are playing against, in duplicate bridge the goal is to do better than other pairs playing the exact same cards. Because of this, strategies are different. In rubber (like in IMP scoring), 30 points above the line for an overtrick is unimportant and hardly worth risking a set. In match-points duplicate, it is common for those 30 points to mean you get a top score instead of average ? and may be worth risking going down. In rubber, an occasional 800-point penalty is disastrous, but on matchpoints it is no worse than any other bottom score. International match points is in the middle of these extremes. Huge penalties are worse than small penalties, but then 30 point differences are only moderately important.

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 with the minimum bid. In rubber bridge, it may often 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 which has gotten bad cards all night may still have the high score for the evening ? so long as they play those cards better than the other pairs with the same cards.