kennyp

With due respect to whoever developed the Neuberg formula I think it is flawed. Any process designed to level the scores for boards played an uneven number of times should still respect some aspects of the original scores. The example given in the explanation of the Neuberg formula illustrates my concern. When played 10 times the person who got the bottom score gets zero matchpoints. But if you were expecting the board to be played 11 times that zero becomes 0.1. This doesn't make sense to me. A bottom is a bottom and should stay at zero. The original top score of 18 shouldn't become 20 so 19.9 seems OK and prorating the extra points to other pairs seems to work until you get to the bottom. The issue for me is to try and adjust scores and total results fairly for a bridge club that normally has between 10 and 15 tables. We usually have 24 to 33 boards in play. Invariably the boards are not all played the same number of times. This may be due to the fact that some tables don't finish the final round or because some boards are simply missed. I think the ACBL approach of just adding the matchpoints and determining percentages after the addition makes the most sense. I recognize that the differences between the three approaches (calculating percentages and then averaging the percentages, applying the Neuberg formula adding the matchpoints and then taking percentages, or adding the raw matchpoints and then taking percentages) are quite small but I'd like to think that things are done properly and accurately, both at my club and certainly on BBO. For IMP scoring you can apply the same principle that I support for matchpoints . You know the total number of times boards have been played and how many times the boards played by a given pair have been played so you can adjust the scores for each hand at each table accordingly, then multiply the actual results by the "adjustment factor." I have developed an Excel spreadsheet for the scoring and can determine the matchpoint results using each approach. For fun I also included IMP scores using cross IMPs and calculating IMPs on the average score,and net points. Barmar mentioned the advantage of using percentages because they are better understood by players and I agree with that. My solution is to present the percentage scores for each hand and also for the final results. But the final results are not the average of the percentages but are determined by using the matchpoints in the background. By the way, as a side issue, does anyone know if some clubs are changing to IMP scoring over matchpoints. With computerized scoring it seems to make sense to me.

On BBO you convert the matchpoint scores to percentages before totalling the matchpoints. Then when you average out the percentage scores for each hand I think you treat them equally. This is OK if the boards have been played the same number of times but not when the boards have been played different times. The percentage scores are valid to evaluate how well a pair may have done on a given board but they are not valid to use when adding results up for a number of boards. You have to use the actual matchpoints. A board played 12 times will result in a maximum of 11 matchpoints while a board played 11 times has a maximum of 10 points. The maximum percentage in both cases is 100 but the matchpoint scores differ. This impacts the results when the scores are added together. For example suppose two teams are discussing how they did in a recent bridge session and they focus on two tricky boards (say boards 1 and 2). Team AA got an absolute top on board 1 and an absolute bottom on 2. Team BB did exactly the reverse: a bottom on 1 and a top on two. So they would each get 100% and 0% which would average out to 50% and conclude that they tied on these two boards. But suppose board 1 had been played 12 times while board 2 had only been played 11 times (a common occurrence at most bridge clubs and certainly very > common on BBO). ACBL scoring would give AA 11 points for board 1 and 0 for 2. BB would get 0 points for board 1 and only 10 for board 2. If you then calculated percentage scores AA would get 11/21*100 or 52.38% and BB 10/21*100 or 47.62%. When you score a larger number of boards the difference is not going to be as large as this but there is still going to be a difference. A similar issue occurs with IMP scoring. If you average a score and treat it the same as other scores when adding them together you skew the results. For board played 12 times, if a NS pair beats all other NS pairs by 3 IMPs they would gain a total of 33 IMPs. If you take the average of this result it would be 33/11 = 3 IMPs. For another board played 11 times if the NS pair again wins by 3 IMPs versus all other pairs they would gain 30 IMPs and an average of 3 IMPs. If you add the averages the scores would be tied 3 to 3. But the real result is that one pair is ahead by 3 IMPs, 33 minus 30.