IMP Pairs Scoring
by Gordon Rainsford

The traditional method of scoring duplicate pairs games has always been Match-Points – so much so that it is often called Pairs Scoring. However, there is no reason why that should be the only method used by clubs, and for those who would like to play something that feels rather more like a teams game (without the bother of organizing team-mates), it is possible to score pairs games by IMPs. Nowadays many players will have encountered this form of scoring when playing online, where it is extremely popular indeed.

From the players’ point of view, the main difference is that, as when playing teams, it is important to bid games (especially when vulnerable) and to a slightly lesser extent it is important to bid slams, but it’s not worth risking a contract for overtricks. It’s still often right to try to get as many tricks as possible – don’t give up just because you have made your contract, but don’t ever risk going down for the sake of an overtrick. Whatever you do though, make sure you avoid going for a large penalty. Sacrificing and protective bidding are often rather too risky to be worthwhile at IMPs.

For the organizers and scorers, all that is needed these days is to tell the scoring program that you want to play an IMP game, and let the computer do the rest. Remember to switch off the percentages if you score with Bridgemates (and remember to switch them back on afterwards)!

Originally, IMP pairs games were scored by the Butler method (named after Geoffrey Butler, a former president of the now-defunct British Bridge League who devised the method as a means of scoring British international trials). This method establishes a 'datum' for each board, by averaging the scores achieved across the field (sometimes discarding the top and bottom one or two scores first). Then the players’ scores are compared to the datum, and the difference converted to IMPs using the normal scale.

However, there are a few problems and anomalies with this method, and nowadays it’s generally considered better to use the alternative Cross-IMPs method – especially since that’s the way most of us who have played online have encountered IMP scoring. Cross-IMPs simply scores each result in IMPs against all the other results in the field, and then takes the average of them. In the old days this would have been quite a task to do by hand, which is probably why the Butler method was used for so long, but with computer scoring Cross-IMPs is quite straightforward – just select the appropriate setting in the scoring program, and let it do the rest.

For clubs that are looking for something different for their games, either for one night a week if they have several regular games, or for an occasional special event, I thoroughly recommend IMP-pairs. At the Young Chelsea Bridge Club where I am the club manager, we have had a weekly IMP-pairs game on Fridays for nearly thirty years, and it is by far the most popular game of the week. Originally it was scored as Butler, but for the last six years or so we have used Cross IMP scoring (in terms of players’ tactics, there isn’t really any difference between the two). The members seem to enjoy not only the variety, but also the fact that some boards have greater importance than others. Slam hands and wildly distributional hands really do have more effect on your result than balanced part-scores when scoring by IMPs.

One result of this is that there is a degree of luck which boards you play sitting in which direction (if you have a one-winner movement), and to some extent which boards you play against whom. Of course that also applies in match-pointed pairs, but then the boards all have the same value, whereas in IMPs one very good or bad board can cancel out several others. If you are very concerned about this effect for a serious event you should try to play a full Howell, or a two-winner movement in which everyone plays exactly the same boards and the field is carefully spread out according to strength – “seeded”. This is not practical for most club games, and having a bit of luck involved doesn’t usually detract from the fun, but it’s a good idea to avoid having too many spare board-sets in circulation (a Web Mitchell can help with this if you have a large field), so that everyone gets to play the swingy boards as well as the flat ones.