Scoring

IMPs vs MP

The following link may be useful. Not written by AI. See also the addendum (some notes added by me).

https://pi.math.cornell.edu/~belk/impmp.htm 

For now, the text below is generated from AI for convenience sake

Qn: can you explain how match point scoring works 

Match point scoring is the most common form of scoring for duplicate bridge, which is the type of bridge played in most clubs and tournaments. Unlike rubber bridge, where you accumulate points over a series of hands, match points evaluate each hand (or "board") independently.

Here's how it works:

The Core Concept: Relative Performance

Match point scoring is all about how you perform compared to the other pairs who played the same hand. It doesn't matter how high your absolute score is; what matters is your rank among the scores achieved by other pairs.

For each board, you receive points based on this ranking:

• You get 2 match points for every pair in your direction (North-South or East-West) that you beat.

• You get 1 match point for every pair you tie with.

• You get 0 match points for every pair that beats you.

An Example

Let's imagine you are a North-South pair, and there are 6 tables in the room. This means 5 other North-South pairs played the same hand as you.

Let's say the final scores for all the North-South pairs on a particular board are:

Now, let's calculate the match points for each pair:

• Pair C (+450): This is the highest score. They beat 5 other pairs.

  • Match Points: 5×2=10

• Pairs A & B (+420): These pairs tied for the second-highest score. There are 3 scores below them.

  • Match Points: They each beat 3 pairs (3×2=6) and tied with 1 pair (1×1=1). The total is 7 match points. The standard way to calculate this is to add up the available match points for the positions they would have occupied (in this case, 8 for 2nd and 6 for 3rd) and divide by the number of pairs that tied. So, (8+6)/2=7.

• Pair D (+400): This pair is in fourth place. They beat 2 pairs.

  • Match Points: 2×2=4

• Pair E (-50): This pair is in fifth place. They beat 1 pair.

  • Match Points: 1×2=2

• Pair F (-300): This is the lowest score. They were beaten by 5 pairs.

  • Match Points: 0×2=0

At the end of the session, each pair's match points from all the hands they played are added up, and the total is converted to a percentage. The pair with the highest percentage wins.

Key Strategic Implications

Because every hand has the same weight (it's either a win, a loss, or a tie, regardless of the score difference), match point scoring leads to a different strategy than other scoring systems like IMPs.

• Overtricks are crucial: An overtrick that no one else gets can be the difference between an average score and a "top board," a score that beats all others.

• Small point differences matter: A 10-point difference (for example, making 3NT instead of 5 of a minor) can be enough to beat a rival and earn you valuable match points.

• Minimize your losses: If a contract can't be made, your goal is to go down by the minimum number of tricks. Going down one trick when everyone else goes down two can be a great result.

• Aggressive bidding and penalties: Match point players are often more willing to compete for part-scores and make penalty doubles, as the risk of a slightly larger loss is often outweighed by the chance of a good score.

Qn: in contract bridge, how does imp scoring work 

In contract bridge, IMP (International Match Point) scoring is a method used to convert the point difference between two scores into a more standardized measure. This scoring system is most commonly used in team events and some pair events.

Unlike matchpoint scoring, where your score on a board is compared to all other pairs who played the same hand, IMP scoring focuses on the magnitude of the score difference. The key is to compare your result with the result of another team or the average of a group of players.

Here's a breakdown of how it works:

1. Calculate the Raw Point Difference: The first step is to determine the difference between the two scores. In a team event, this is a head-to-head comparison between the scores of your team's two pairs. For example, if your North-South pair scores +420 and your teammates playing East-West on the same board score -170 (because the other team's North-South made a partscore), the net difference is 420−(−170)=+590 points.

2. Convert to IMPs: This point difference is then converted to IMPs using a standardized table. The table is designed to diminish the impact of very large and very small score differences. This means that a huge swing (like a slam going down) won't have the same overpowering effect it might in other scoring systems.

Here is a simplified version of an IMP conversion table:

So, using the example above, a point difference of 590 would convert to 11 IMPs. Your team would be awarded +11 IMPs and the opposing team would receive -11 IMPs for that board.

Why IMP Scoring Changes Strategy

IMP scoring significantly influences bridge strategy compared to matchpoint scoring.

• Focus on Games and Slams: The biggest rewards in IMP scoring come from bidding and making game and slam contracts. The bonus for making a game is significant, and the point difference between a game and a partscore can be a huge number of IMPs.

• Overtricks are Less Important: In matchpoint scoring, an overtrick can be the difference between a top and a bottom score. In IMPs, the extra points from an overtrick often fall within the same IMP range, so they are not worth risking the contract itself. The primary goal is to make your contract.

• Conservative Play: Declarers are encouraged to play safely to ensure they make their contract, even if it means forgoing an attempt at an overtrick. Similarly, defenders should prioritize defeating the contract rather than trying to limit overtricks.

• Risky Bids are More Rewarding: When considering a marginal game, especially when vulnerable, the potential gain from making the game is much larger than the potential loss from going down. This encourages bidding "thin" games that may only have a 40-50% chance of success.

Addendum - accumulative vs non-accumulative scoring

MPs are non-accumulative. This means a bad board score stays within that board mostly. 

Let's say you have the following 4 board scores:
50%

100%

0%

50%

Your total MP score is 200/4 = 50%. You can't score more than 100% or less than 0%. Also, if you score 50% instead of 0% in the 3rd board. Your total MP score is then 250/4=62%. your 50% score contributes 50/4 of the difference. in a 24 board tournament, that 50% swing contributes 50/24 = 2% difference only). 

But the same boards when calculated in IMPs might be:
+1

+8

-15

+0

Total -6 IMPs

Exactly the same result in raw score but in MPs, you are basically "average". In IMPs, you are down -6. The reason is that IMP scores are absolute and accumulative. That single bad score of -15 carries through on your total score. In MPs, that bad board is limited to 0%, which is averaged.