近来不少网友询问BBO是如何计算每一副牌的IMP得分。特此解释一下。

Here's how BBO's IMP scoring system works. Assume you are sitting North-South, play board 1 and get a score (say, for example, you bid and make 3NT and score +400). Your +400 is then IMPed (using the IMP scale) against all the other North-South pairs who played board 1. At BBO's Main Lobby, each board is played exactly 16 times. Your +400 is compared 15 times with the scores of the other 15 North-South pairs (using the IMP scale). The IMPs you won or lost in each of these comparisons is added up and then divided by the number of comparisons (which is 15). The result is your partnership's IMP score for board 1.

After you have played a deal, it will normally be played by other tables as well. When their score is computed, your score may change as a result. BBO updates your score automatically. This is also why you sometimes think, "Wow! We just got +800 against a partial, why did we get zero IMPs for it?". The reason will usually be that you were the first table to play the deal.

For IMP pairs tournaments, the same scoring method is used (the number of comparisons for each board equals the number of tables minus 1).