Main     Article 7Q42 by Richard Pavlicek    

Instant Matchpoints 1997

On Wednesday evening, September 17, players throughout ACBL-land will compete in the 11th annual Instant Matchpoint Pairs. Check with your local bridge club for the playing site nearest you. Don’t miss it!

Just what are “instant matchpoints” anyway? This article should provide some insight into this unique scoring method and the preparation behind it.

Most matchpoint events are scored by the actual results of each participant, i.e., each section (or group of sections) is matchpointed to determine the awards. An instant matchpoint event is different: The matchpoint awards for every possible result are predetermined. For example, if you bid and make 4 S on a particular board, you will look up your score in a chart to find your matchpoint award immediately.

Which is better? On a strictly comparative basis, the regular method is superior because it is based on the actual results of the participants. But instant matchpoints are fun! Besides being able to look up your score right away, these events are usually accompanied with written analyses. You can read about the deals you played and often gain tips to improve your game.

The most difficult task for an instant matchpoint game is to prepare the scoring awards. No matter how this is done, it cannot be completely fair because no one can predict the future; it can only approximate fairness. In most cases (as in the upcoming ACBL event) the scoring awards are based on actual results when identical boards were played in another event. Of course, this has to be a foreign event and preferably long past to minimize the chance of anyone replaying and remembering the boards.

How are the matchpoint awards prepared? How can you determine an award for every possible result? I will explain the steps I follow using a hypothetical example. Assume Board 1 was previously played 180 times with the following data, which has been matchpointed in routine fashion with 179 top:

N-S ScoreFrequencyMatchpoints
+9804177.5
+8003174
+4808168.5
+45026151.5
+42011581
+400620.5
-50179
-10010

The above matchpoints will not suffice on a general basis. What if a N-S pair scores +500, or -150, or any other result not shown? What do they get? Well, you could refund their entry fee and tell them to try again next year — or you could adjust the table to account for the gaps.

The method I use is to assume a “mystery score” as part of the original data, thus increasing the top by one. Every existing score is presumed to have tied the mystery score (thus adding 1/2 matchpoint to each), then every possible gap is matchpointed in normal fashion. The table then becomes:

N-S ScoreFrequencyMatchpoints
180
+9804178
176
+8003174.5
173
+4808169
165
+45026152
139
+42011581.5
+400621
18
-50179.5
1
-10010.5
0

Note how the top gap gets 180 (the new top) since it beats every real score, and the bottom gap gets zero. The gap between +420 and +400 would be worth 24 matchpoints, but there is no way for anyone to score +410 so it is eliminated from the table.

This method would produce different tops on many boards, so the awards are converted to a percentage (or 100 top) for uniformity. Fractional percentages are rounded to the nearest whole percent, producing:

N-S ScoreFrequencyPercent
100
+980499
98
+800397
96
+480894
92
+4502684
77
+42011545
+400612
10
-50175
1
-10010
0

Oops. The percentage for -100 rounds to zero, just like the bottom gap. This is acceptable, but it seems wrong and is esoterically displeasing to give the same award for different results. Hence I would smooth out the last three awards to become 2, 1 and 0.

As a final step, I occasionally adjust the matchpoints if I feel the results are biased by non-American systems, or if I feel our players would generally bid better. For example, say a N-S slam contract happens to earn 96 percent (giving the poor E-W victims only 4 percent) and I think the slam would be bid more often; I would use my judgment to lower the award slightly. I make these adjustments sparingly, and never by more than 10 percent.

Even with a protracted attempt to produce fair scoring awards, one cannot please everyone — so what else is new? Therefore, to eliminate potential bias, the ACBL goes one step further: The N-S and E-W fields are scored independently to produce two separate winners. Thus, if a board turns out to be biased, it will affect everyone in your field equally.

So mark September 17 on your calendar! Get out and play! I can’t give you any previews of the deals (ha), but I’m sure you’ll have a great time.

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© 1997 Richard Pavlicek