My partner and I have just started playing bridge, and played our first event yesterday. It was Swiss Pairs, where you play several boards against another pair, and then they work out scores and rematch you to someone around your level for the next round. At the end of each round, they give you a piece of paper with your results. It has columns:
Contract Tricks Score Datum Net Imps
The first 3 columns I understand. The datum is apparently the average score. The Net looks like your score added to the datum. Imps are related to this net score somehow. The actual final results are based on VPs, which are something else again.
I don’t understand why there are 3 additional ways of working out the score (net, imps, VPs). Even more confusing, why do they add everyone’s score to the average score? Doesn’t this give basically the same list of scores, just with them all shifted by the same amount? I asked a couple of people at the event, including the organiser, but they just went away when I asked why those two numbers are added together.
I cannot say exactly how the swiss pairs method achieves the result, but here are the basic meanings:
Score is your score for the hand, based on standard contract bridge scoring.
Datum should be the average score for that hand across all pairs playing the hand.
Net should not be additive, but subtractive. Your result versus the average result.
IMPs means International Match Points. They are a method of comparing bridge results that takes into account that doing fantastically better (or fantastically worse) than the average on one hand shouldn’t have an over-whelming effect upon the result of the round. So there is some sort of logarithmic scale used that gives a lot of points for making a contract that others don’t, but doesn’t give you that many more for making a slam on the same hand.
The way I’ve played and scored Swiss is that your team of four plays another team of four once playing N-S once playing E-W. “Net” is the difference between your scores. So if you bid and made 4S vul you’d score 620. If your partners sacrificed in 5D down 2 for -200, your net would be 420. You then need to look up what 420 is in IMPs. You need a table for this, though I expect those you play often know it.
IMPs are net IMPS
20-40 1
50-80 2
90-120 3
etc.
IMPs are used so that a huge win on one hand (You make 6S vul. Your opponents are down 1 in six spades vul. doesn’t dominate the entire score. It’s sort of halfway between rubber bridge scoring and standard duplicate scoring where it doesn’t matter if you win by an overtrick or 1100, you just win that hand. With Imps the scale is a concave award so you get fewer additional IMPs for going from 420 to 450 than for going from 20 to 50.
Victory points are a conversion from IMPs. Those are usually either on either a 30 point or 20 point basis. All 30 or 20 points are awarded to one team or the other. I don’t really know why the second conversion is used.
They play Swiss teams sometimes too. For pairs, it’s like everyone has the average as their partner. Maybe they just need to do that to make the computer program work.