Duplicate bridge is the name given to organised bridge tournaments as opposed to social or rubber bridge which involve just four players. The main kinds of competitive bridge are pairs events and teams events.
The advantage of duplicate is that the element of having good cards or bad cards is reduced to a minimum, since in general all players play exactly the same deals. Duplicate also improves your game, since the hand records are available to check afterwards where you may have gone wrong.
There are some vital differences between duplicate and ordinary (rubber) bridge in regard to technicalities and strategy. Except at the first table, you will not shuffle and deal the cards. The cards come to you in a tray, called a 'board' and you must put the cards back in the correct slot after the board has been played. The board is marked N, E, S and W, and must be placed properly on the table; the board also states which side is vulnerable and who is the dealer. During the play, the cards are not thrown into the middle of the table. The players keep their own cards in front of them, turning the card played face down after the trick is over. Tricks won are placed in front of you and perpendicular to the edge of the table. Tricks lost are placed in front of you and parallel to the edge of the table. After each deal is over, you still have your original thirteen cards in front of you and can see at a glance how many tricks have been won and how many lost.
Each board in tournament bridge is scored independently. In rubber bridge if you make a partscore you have an advantage for the next deal, but in tournament bridge you do not carry forward any scores. You enter the score for the hand played, and on the next board both sides start from zero again.
As each deal is totally unrelated to what happened
on the previous deal, there are significant scoring differences at duplicate:
(1) Honours do not count.
(2) For bidding and making a partscore, add 50 to the trick total.
(3) For bidding and making a game not vulnerable, add 300 to the trick total.
(4) For bidding and making a game vulnerable, add 500 to the trick total.
The result you obtain on the board is entered on the 'travelling score sheet' at the back of the board. You may not look at that until the hand is over, since it contains a record of the hand and also how other pairs fared on the board.
Your score on each board is compared with the scores of every other pair that played the board. If you are North-South, your real opponents are all the other North-South pairs, not the particular East-West pair you played each time. On each board, a certain number of matchpoints is awarded. You receive 2 points for each pair whose score you beat, 1 point for each time you tie with the score of another pair and 0 for each pair whose score beats yours.
The scoring is done once for the N-S pairs and then for the E-W pairs. Each pair's points over all the boards are totalled and the pair with the highest number of points wins.
Tactics in pairs events differ from those in rubber bridge. Careful declarer play and defence are the order of the day. Every overtrick and every undertrick could be vital. They make the difference between good scores and bad scores. Being extermely competitive in the bidding is essential. Minor suit contracts at the game zone should be avoided. Prefer 3NT to 5C or 5D, even if 3NT is riskier, since making an overtrick in 3NT scores more than a minor suit game.
Extract from: Guide to better duplicate bridge, Ron Klinger.