The are two main differences between duplicate and teams events.
This is done by taking the results of boards played between the N/S and opposing E/W, and the same board played by the other pairs in those teams.
As an example, N/S team 1 play boards 5>8 against E/W team 3. Also N/S team 3 will play boards 5>8 against E/W team 1. A score can be calculated across each of these 4 boards.
This will continue throughout the evening. Scoring is done using IMPs method (Internatonal Match Points).
Using a single board as an example. If N/S team 1 score 90 points (1NT bid and made) against E/W team 3 and the opposing pairs N/S team 3 against E/W team 1 also score 90 points then they cancel each other out and the combined score is 0 (N/S team 1 +90, E/W team 1 -90).
If however there are different results N/S team 1 score 600 (3NT bid and made) against E/W team 3 but the opposing pair N/S team 3 scores 150 (2NT bid and made 9 tricks) then there is a difference. N/S team 1 = +600 E/W team 1 = -150 giving a net score to team 1 of +450. Team 3 N/S scored -600 and their E/W scored +150 giving a net -450.
The difference on each board e.g. +450 for Team 1 and -450 for Team 3 is then converted to IMPs using a cross reference table. This is on a separate page.
The scoring continues for each board. It should be noted that the results of team 2 playing team 3 do not impact on the results of team 1, other then the total number of IMPs scored. It is a 'battle' of the boards played between the pairs of opposing teams that is important.
In Duplicate the results can be very different when a pair manages to get a single overtrick.
In an event where a board is played 6 times, if most pairs bid and make 3NT for a score of 400 and one pair achieves an overtrick, that one pair will score 10 points and all other pairs will score 4 each. Even worse for the opposing pair who will get zero. Other pairs will get 6 points.
In IMPs scoring, the difference is less dramatic. As can be seen from the IMPs table, if there is a difference of 30 points between opposing sides on a particular board, it will only result in a difference of 1 IMP. What is important is that it is not worth risking a contract to achieve an overtrick. Bidding and making a contract is far more important. The other significant thing is to ensure that a game contract is bid if possible. Once bid, make the contract and do not try for overtricks, similarly for slam bidding.
As can be seen from the IMPs table there is a great advantage in bidding (and making of course) game and slam contracts in case the opposing pair do not bid the game/slam. The difference of 450 points (as in the example above) would score 10 IMPs for Team 1 and -10 IMPs for Team 3.
The strategy then becomes more complicated. If non-vulnerable should I risk bidding game to achieve 400 points or stick to 150 (3NT - 9 tricks vs 1NT - 9 tricks). Here the difference is 250 points = 6 IMPs (if game was made). However if Vulnerable the difference would be 10 IMPs. Maybe worth the extra risk ???