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IMP Scoring

#1 User is offline   tar400 

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Posted 2018-February-14, 11:11

I have always played contract bridge and most people on BBO use IMP Scoring. I have looked on the internet for help but am certainly confused. Example: Contract is 4 spades and the score is 620. How did you come up with 620? Then there is a conversion to IMP. I can probably figure out the conversion (maybe lol) if I see how 620 is made. Thanks. I have no idea how to check back and see if anyone answers this. New to BBO Thank you!
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#2 User is offline   Cyberyeti 

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Posted 2018-February-14, 12:06

View Posttar400, on 2018-February-14, 11:11, said:

I have always played contract bridge and most people on BBO use IMP Scoring. I have looked on the internet for help but am certainly confused. Example: Contract is 4 spades and the score is 620. How did you come up with 620? Then there is a conversion to IMP. I can probably figure out the conversion (maybe lol) if I see how 620 is made. Thanks. I have no idea how to check back and see if anyone answers this. New to BBO Thank you!


OK, 620 is 4x30 for 4 +500 for a vulnerable game (300 for a NV game to simulate the value in rubber). The IMP scale is designed to avoid one hand having a disproportionate effect, the way you use it is to compare scores. You score 620, the other table in your teams match opps didn't bid game and scored 170 (120 +50 for a part score), difference is 450, look that up on the IMP scale = +10.

IMP pairs you compare your score to the average of what other pairs in your direction scored then use the IMP scale (possibly dropping the best/worst one or two in each direction before averaging depending on numbers).
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#3 User is offline   Vampyr 

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Posted 2018-February-15, 07:16

View PostCyberyeti, on 2018-February-14, 12:06, said:

IMP pairs you compare your score to the average of what other pairs in your direction scored then use the IMP scale (possibly dropping the best/worst one or two in each direction before averaging depending on numbers).


This method of scoring is called Butler and its pretty rare these days. Now, IMP Pairs are scored by cross IMPs, in which your score is compared to the score of each of the other players in your direction, sometimes divided by the number of pairs. No scores are dropped.
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#4 User is offline   Cyberyeti 

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Posted 2018-February-15, 08:12

View PostVampyr, on 2018-February-15, 07:16, said:

This method of scoring is called Butler and its pretty rare these days. Now, IMP Pairs are scored by cross IMPs, in which your score is compared to the score of each of the other players in your direction, sometimes divided by the number of pairs. No scores are dropped.


Cross IMPing and dividing looks suspiciously similar to a Butler with no dropped scores, is why I used the word possibly
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#5 User is offline   NickRW 

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Posted 2018-February-15, 08:35

View PostCyberyeti, on 2018-February-15, 08:12, said:

Cross IMPing and dividing looks suspiciously similar to a Butler with no dropped scores...


For most practical purposes they are the same - but the calculations are different and can lead to "anomalies" when one expects them to be the same and they are not.
"Pass is your friend" - my brother in law - who likes to bid a lot.
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#6 User is offline   helene_t 

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Posted 2018-February-15, 18:40

Cyberyeti's explanation is correct for team matches and for butler (butler is not played on BBO).

Cross-IMP is not the same as butler (even without removing outliers). In cross-imps (or IMP Pairs at it is called on BBO), your score is compared to each of the other pairs in the same direction.

Suppose you score +620 while there are two other pairs in the same direction who scored +650 and +170, respectively. You win 10 IMPs from the +170 pair and lose one IMP to the +650 pair. This gives an average of (10 + -1)/2 = 4.5 and this is the IMPs that will be shown on BBO.
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#7 User is offline   Cyberyeti 

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Posted 2018-February-16, 05:36

View Posthelene_t, on 2018-February-15, 18:40, said:

Cyberyeti's explanation is correct for team matches and for butler (butler is not played on BBO).

Cross-IMP is not the same as butler (even without removing outliers). In cross-imps (or IMP Pairs at it is called on BBO), your score is compared to each of the other pairs in the same direction.

Suppose you score +620 while there are two other pairs in the same direction who scored +650 and +170, respectively. You win 10 IMPs from the +170 pair and lose one IMP to the +650 pair. This gives an average of (10 + -1)/2 = 4.5 and this is the IMPs that will be shown on BBO.


You are correct but much of the time the results are pretty similar, in that example you give the result of doing it the other way would be 620-410 = 210 = 5 IMPs
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#8 User is offline   NickRW 

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Posted 2018-February-16, 05:54

View PostCyberyeti, on 2018-February-16, 05:36, said:

You are correct but much of the time the results are pretty similar, in that example you give the result of doing it the other way would be 620-410 = 210 = 5 IMPs


As I understand it, the "datum" in the Butler method is 620+650+170/3 = 480 (i.e. includes your score), not 650+170/2 = 410. One could argue your method is better, but would require a different datum for every table and the Butler method was created for IMPing a pairs event in the days before computer scoring.
"Pass is your friend" - my brother in law - who likes to bid a lot.
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#9 User is offline   Cyberyeti 

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Posted 2018-February-16, 06:14

View PostNickRW, on 2018-February-16, 05:54, said:

As I understand it, the "datum" in the Butler method is 620+650+170/3 = 480 (i.e. includes your score), not 650+170/2 = 410. One could argue your method is better, but would require a different datum for every table and the Butler method was created for IMPing a pairs event in the days before computer scoring.


Sorry, you are correct, I'm posting without being properly awake, builders next door getting me up 2 hours earlier than I wanted to, still 4 IMPs though which makes the point that the result is similar.
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