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How ACBL strata work

#1 User is offline   pilowsky 

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Posted 2020-September-08, 22:06

A moment ago I played in an ACBL IMP's robot challenge tournament. I had a lot of fun and manage to scrape together +1.78 IMP's for no masterpoints. But 5 people who scored lower than me did get masterpoints.
Undeterred I went to the University and asked Mr Wang from the Institute of Systems Engineering how this could happen.
Don't worry he said I'll explain it with a few simple equations.
It took a few moments, but he quickly put my mind at ease.
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#2 User is offline   mallymarom 

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Posted 2020-September-09, 02:23

high level astrophysical bridge. we all can learn here
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#3 User is offline   pilowsky 

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Posted 2020-September-09, 02:54

View Postmallymarom, on 2020-September-09, 02:23, said:

high level astrophysical bridge. we all can learn here


I know what you mean, at first I thought it was going to be complicated. Mind you, I had to help him out with equation 14.
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#4 User is offline   aawk 

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Posted 2020-September-09, 05:55

Is it possible those players where playing in a different group and scores where calculated for each group.
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#5 User is offline   SelfGovern 

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Posted 2020-September-09, 11:15

There are several ways to get points in the tournaments on BBO.
There are first of all overall awards -- the best score out of everyone gets the most monster points.
The second-best score out of everyone gets the second most monster points.

Then there are section awards. When the game starts, people are somewhat randomly assigned to "sections" of (typically) 12 - 15 tables. The sections are given letters (A, B, C, ...). People in section A only play against others in section A.

After finding the overall awards, players in each direction (N/S or E/W) of each section are then ranked. The top scoring pair of section A N/S is given the better of the section 1st award or their overall place., and so on for each section and each direction, until all the places have been awarded.

It is certainly possible that in your event, your score was not good enough to place in your section. Or, the pair that won points could have been in a lower flight than you were (it takes a better score to place in flight A than in flight C, see below).

All of the ACBL events on BBO, and most of the non-ACBL BBO tournaments then stratify the game -- putting players into groups based on the number of points each pair has. Let's say that the top 1/3 (5) of a 15-table section are classed as Flight A. Then the remaining (10) pairs are ranked 1st through n for the "best in flight (or strat) B" award. Finally, those who have too many points for flight C are removed, and the remaining five pairs are awarded the highest monster point award they qualify for.

Note that a Flight C pair can win 1st overall, or second in their section for flight A or B, and they would get the highest award they qualify for (not the sum of possible awards).

A C pair can win a C award or a B award or an A award or an overall award. A B or A pair cannot win a C award.

I hope this helps.
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#6 User is offline   pilowsky 

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Posted 2020-September-09, 13:07

View PostSelfGovern, on 2020-September-09, 11:15, said:

There are several ways to get points in the tournaments on BBO.
There are first of all overall awards -- the best score out of everyone gets the most monster points.
The second-best score out of everyone gets the second most monster points.

Then there are section awards. When the game starts, people are somewhat randomly assigned to "sections" of (typically) 12 - 15 tables. The sections are given letters (A, B, C, ...). People in section A only play against others in section A.

After finding the overall awards, players in each direction (N/S or E/W) of each section are then ranked. The top scoring pair of section A N/S is given the better of the section 1st award or their overall place., and so on for each section and each direction, until all the places have been awarded.

It is certainly possible that in your event, your score was not good enough to place in your section. Or, the pair that won points could have been in a lower flight than you were (it takes a better score to place in flight A than in flight C, see below).

All of the ACBL events on BBO, and most of the non-ACBL BBO tournaments then stratify the game -- putting players into groups based on the number of points each pair has. Let's say that the top 1/3 (5) of a 15-table section are classed as Flight A. Then the remaining (10) pairs are ranked 1st through n for the "best in flight (or strat) B" award. Finally, those who have too many points for flight C are removed, and the remaining five pairs are awarded the highest monster point award they qualify for.

Note that a Flight C pair can win 1st overall, or second in their section for flight A or B, and they would get the highest award they qualify for (not the sum of possible awards).

A C pair can win a C award or a B award or an A award or an overall award. A B or A pair cannot win a C award.

I hope this helps.


Your further explanation only muddies the waters. I thought Mr Wang had made it pretty clear.
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#7 User is offline   Vampyr 

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Posted 2020-September-09, 13:14

Can a B or C pair be awarded masterpoints if their score is below average?
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#8 User is offline   PrecisionL 

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Posted 2020-September-09, 14:48

View PostVampyr, on 2020-September-09, 13:14, said:

Can a B or C pair be awarded masterpoints if their score is below average?


Yes, this can happen inf Flight C frequently.
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#9 User is offline   SelfGovern 

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Posted 2020-September-09, 16:29

View PostVampyr, on 2020-September-09, 13:14, said:

Can a B or C pair be awarded masterpoints if their score is below average?


In an ACBL IMP tournament, I recently had a friend get masterpoints for placing in strat B with a -3.x IMP score. It can easily happen if all the As beat every B.
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#10 User is offline   pilowsky 

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Posted 2020-September-09, 16:42

It's a remarkably democratic format. A few weeks ago I beat ###### and so that means I'm the North American Bridge Champion. The next week I beat @@@@@ making me the online Bridge champion. Mr Wang says that if I change my birth certificate and move to New York, Rudy will help me become President of the USA. How about that?
Oh look, 5 minutes ago I just got 0.37 masterpoints for coming 9th. The person who came 8th got 0.11, the person who came 17th got 0.26.
Now I understand the Electoral College.
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#11 User is offline   mallymarom 

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Posted 2020-September-10, 00:21

[c
Your further explanation only muddies the waters. I thought Mr Wang had made it pretty clear.
[/quote]
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#12 User is offline   blackshoe 

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Posted 2020-September-10, 08:56

Keep in mind that "Flight A" and "Stratum A" don't mean the same thing. B-)
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#13 User is offline   Vampyr 

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Posted 2020-September-10, 13:16

View PostSelfGovern, on 2020-September-09, 16:29, said:

In an ACBL IMP tournament, I recently had a friend get masterpoints for placing in strat B with a -3.x IMP score. It can easily happen if all the As beat every B.


Yes, of course. I was wondering whether there was a regulation that prevented masterpoints being given. It seems like there should be.
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#14 User is online   mycroft 

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Posted 2020-September-11, 09:27

My Tuesday night game back at the old club was interesting. Averaged 8 tables or so, pretty equally grouped into City Championship contenders and pairs just out of the protected games (which weren't mid-flight games like they are now). Nothing in the middle. The new players came to this game because I enforced a "beat them, but no game-playing" rule. No lessons without a request, no "DIE-REK-TOR", no "that's Just Bridge",... It was well known as "the game to go to to get your feet wet in the Open", even though the open pairs that were there were - very strong.

Therefore, on the days when we had 9 A pairs and 5 new pairs, there were definitely times where 48% was a great game for the new pair. The rest of them were around 40%.

Don't see why just because they didn't hit a magic number we shouldn't reward the "winner" of the lower strat.

There are games I've had where I "wanted to send back the masterpoints" - but that's because I consider myself an A player, and when we get put into B (or C) and score in that strat with a horrible game, bleah. But I'm not a new player to the open, or a 751 player we're trying to keep playing now that they've aged out of the Gold Rush.

First in B is an accomplishment. First in B that didn't make average (or first in X with -1.45 IMPs in our Sectional IMP pairs) is still an accomplishment. The ones for whom cracking average is their goal will be disappointed; the ones for whom it's their first X award ever, and it's first, will not.
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#15 User is offline   barmar 

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Posted 2020-September-12, 10:29

Mycroft understands the logic of stratification.

The C players are expected to do poorly when playing in an open game, we don't want to penalize them for playing up. So they get points for doing the least poorly of all the C players. And if a C player manages to beat enough A or B players they get even more points, since they're doing far better than their expectation.

#16 User is offline   Vampyr 

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Posted 2020-September-12, 18:57

View Postbarmar, on 2020-September-12, 10:29, said:

Mycroft understands the logic of stratification.

The C players are expected to do poorly when playing in an open game, we don't want to penalize them for playing up. So they get points for doing the least poorly of all the C players. And if a C player manages to beat enough A or B players they get even more points, since they're doing far better than their expectation.


I think that if they want to score masterpoints, they should play in their own game. I imagine that weak players like stratification; strong players do not.
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#17 User is offline   pilowsky 

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Posted 2020-September-12, 19:17

View PostVampyr, on 2020-September-12, 18:57, said:

I think that if they want to score masterpoints, they should play in their own game. I imagine that weak players like stratification; strong players do not.


A real problem with Bridge is the independent calibration of player ability.
Masterpoints have nothing to do with strength - neither do rankings.
Masterpoints are basically entry tickets to competitions so that players can test themselves against other players.
Rankings are a sort of moving average of skill with variable decay time.
A player might play a single hand with extraordinary skill and panache. The next hand you might think the same person was a walking brainstem.
That's why every other sport, without exception, uses a rating system. But, Bridge players know better. What can I say?
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#18 User is offline   sfi 

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Posted 2020-September-12, 21:04

View PostVampyr, on 2020-September-12, 18:57, said:

I think that if they want to score masterpoints, they should play in their own game. I imagine that weak players like stratification; strong players do not.

I'm not sure why the strong players would care that much. If you get too elitist about it, the event shrinks too much. In fact, stratification helps increase skill level in the long run, so it's a good thing for the game.
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#19 User is offline   Vampyr 

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Posted 2020-September-13, 03:56

View Postpilowsky, on 2020-September-12, 19:17, said:

Masterpoints are basically entry tickets to competitions so that players can test themselves against other players.


You don’t need masterpoints to enter the event; you get them at the end.
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#20 User is offline   pilowsky 

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Posted 2020-September-13, 04:19

View PostVampyr, on 2020-September-13, 03:56, said:

You don't need masterpoints to enter the event; you get them at the end.


The ACBL (and all the other organisations) manufacture them wholesale, like the Royal Mint, then retail them to Clubs. Clubs charge players an entry fee for the competition. At the end of the competition, the top players (number varies wildly) get masterpoints. There's even a fixed exchange rate for BBO masterpoints v ABF masterpoints. I think it's 3.5:1.
Masterpoints are like currency except that you accumulate them like barnacles and you can't trade them in for anything useful. Like every other trophy in sport, all you can do is put it on the bookshelf, look at it and say Hmmm. They have no intrinsic value to society. Nobody else wants them. They won't save lives.

At the end of the day, they don't really say anything about the instantaneous ability of the player. That's why a relatively weak pair can win against a strong pair on any given day. Given a combination of the time of day, a hangover and corked red wine.
On the other hand, in a challenge format against robots, it's a much leveller playing field. Assuming that both humans have had some practice playing robot Bridge. But that's a whole different discussion.

The reason that more masterpoints are available in different tournaments is either because:
  • The quality of the candidature is considered to be higher at the start
  • The entry fee is higher. ACBL
  • The number of entrants is large - Daylongs.
  • Some combination of the above.


Mr Wang explained that to me after we went through the equations and finished lunch. It still doesn't make them more useful to man, woman or beast. But people like you and me will still collect them I guess.

So, you do need masterpoints (or something similar) to enter. If masterpoints didn't exist, nobody would turn up. Personally, I think there should be ratings. I think masterpoints are well pointless - see above.
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