Hand Evaluation

[barmar]

The key of IMP scoring is that the actual value of your score is relevant. Of course, IMP-against-median is a way to calculate an IMP pairs, and if people want to play it by all means do, but the fact that it is possible that a large variation in your result doesn't affect your IMP score means that it has little to do with IMP scoring.

But as I pointed out, what matters isn't the actual value of your score, it's the relative value.

 

However, I just did a quick check, and realized that IMP-against-median has a significant difference from cross-IMP: the latter cares about the number of pairs you beat or lost to. With median IMPing, the sizes of the groups of scores can influence which score becomes the median, but then when you compare everyone against it, size no longer matters. With cross-IMP, there's a significant bonus to being the ONLY pair that bids (and makes) the game or slam -- the bonus is multiplied by the number of other pairs (much like getting a top versus just Ave+ in MP). Butler also achieves this, because the size of the other group drags the datum closer to their score. With a median, you get the same number of IMPs no matter how many other pairs there are.

 

The two methods actually produce pretty similar results when the field is evenly split among results. The difference is mostly apparent to outliers.

[Trinidad]

The two methods actually produce pretty similar results when the field is evenly split among results. The difference is mostly apparent to outliers.

Of course, the methods give approximately the same results when the field is evenly split among the results. There is also nothing wrong in using medians to estimate things (life time of a light bulb, amount of food and drinks to be bought before a party, amount of tax you need to pay, ..., or an IMP pair score). Many people do this all the time, but the smart ones are aware that they make an error. Often you don't need to have exact figures. (Does it matter that people drink 2.342643 bottles of wine at my party if I estimated that they will drink between 2 and 3? Either way I will end up buying three bottles.)

 

- Calculating with medians (or modes) is usually easiest, but it will come with the largest error. If this error is perfectly acceptable, by all means ( ;) ) use medians.

- Calculating with averages (more precisely: means), such as Butler, is a little more difficult and will be more accurate. If the calculation that you are performing is linear (IMP scoring is not) you will even get the correct answer: If I know the mean amount of wine that people drink on average, I will be able to tell the total wine consumption by multiplying the mean by the amount of people. However, knowing the mean won't tell me how many people will not be allowed to drive anymore and, therefore, will be sleeping over.

- Calculating with the whole set of results (Cross-IMP) requires more work, but it will give you the correct answer.

 

Rik