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Ever play a game of Rubber Bridge where your opponents got the best cards in their hand through the luck of the deal? Duplicate Bridge removes most of the luck.
In Duplicate, you and your partner are compared with other pairs playing the exact same hands under the exact same conditions. The same hands are dealt on your four-player table and other four-player tables. Determination of vulnerability and the dealer is made before the game. Scores are calculated by comparing your score to those of the other pairs.
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North
10 8
J 8 6 3
A Q 9 4
A K 10
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West
K Q J
K 10 5 4
10 7 6 5 2
6
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East
A 7 5 2
9 2
8
9 8 7 4 3 2
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South
9 6 4 3
A Q 7
K J 3
Q J 5
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For Duplicate Bridge on the Zone, this hand pictured above will be played by up to 24 other pairs. It appears from the cards that the standard result should be 3NT by N/S making exactly 3 for +600 pts. Let's examine the actual score card as played by nine pairs and discuss the various scoring types: Matchpoint and International Matchpoint Scoring.
Matchpoint Scoring
In Matchpoint Scoring, we compare all the scores for N/S -- giving the best N/S score 100% and the worst N/S score 0%. Matchpoints for each pair are determined as follows:
- Calculate the percentage for each pair, where the first-ranked pair with the highest score receives 100% and the lowest-ranked pair with the lowest score receives 0%. All the other pairs' percentages between the first and last are determined by subtracting incrementally the value of 100/(X-1), where X is the number of times the board was played.
- Then average the percentages, if any, where the pair shares the same rank with other pairs.
Let's look at the following example below:
In the example above, the board was played nine times and each position is worth 100/(9-1) = 12.5%. The best N/S score is +630 and receives a top of 100%. Since there were two 630 results, they share 1st and 2nd rank of 100% and 87.5%; where the second rank is 100-12.5 = 87.5. The Matchpoints for 1st and 2nd are (100+87.5)/2 = 93.8 each.
3rd, 4th, and 5th share the same rank because they each have a score of 600. So they share 75%, 62.5% and 50%. Their Matchpoints are ([75+62.5+50]/3), which are 62.5 Matchpoints for 3rd, 4th, and 5th. The passout is next at 37.5% (50-12.5), followed by two 200 scores sharing 25% and 12.5%. Their Matchpoint is 18.8% ([25+12.50]/2). And the lowest score gets 0%.
International Match Point (IMP) Scoring
IMP scoring, originally developed in Vienna, was first used in the 1938 European Championship in Oslo. IMPs are used to flatten the high scores and increase the value of partscore contracts.
To accomplish this we use the IMP scale:
Difference in Points
(between your score and your opponents' score)
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International Match Points
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0-10
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0
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20-40
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1
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50-80
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2
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90-120
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3
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130-160
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4
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170-120
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5
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220-260
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6
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270-310
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7
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320-360
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8
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370-420
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9
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430-490
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10
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500-590
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11
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600-740
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12
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750-890
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13
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900-1090
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14
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1100-1290
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15
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1300-1490
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16
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1500-1740
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17
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1750-1990
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18
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2000-2240
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19
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2250-2490
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20
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2500-2990
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21
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3000-3490
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22
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3500-3990
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23
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4000 and higher
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24
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To calculate your partnership's IMP pairs score, take your score and subtract every other score from it, look the difference up on the IMP table, and sum all these IMPs. Then take the total number of IMPs and divide by the number of pairs to get the IMPs for your partnership. This is called the X-IMP, or cross IMP, method. Still using the score sheet from above for our +630 score we then have:
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630 -
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(+630) =
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0
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= 0 IMPS
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630 -
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(+600) =
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30
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= 1 IMPS
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630 -
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(+600) =
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30
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= 1 IMPS
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630 -
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(+600) =
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30
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= 1 IMPS
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630 -
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(0) =
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630
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= 12 IMPS
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630 -
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(-200) =
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830
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= 13 IMPS
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630 -
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(-200) =
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830
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= 13 IMPS
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630 -
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(-400) =
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1030
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= 14 IMPS
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Total
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= 15 IMPS
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So the IMPs for your partnership are 55 IMPs/8 pairs = 6.88 IMPs
Comparing MP and IMP Scoring
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Raw N/S Score
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MP Score
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X-IMP Score
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630
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93.8%
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+6.88 IMPs
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600
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62.5%
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+6.25 IMPs
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0
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37.5%
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-5.13 IMPs
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-200
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18.8%
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-8.12 IMPs
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-400
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0.0%
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-11.12 IMPs
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