Normalizing averages

[zenko]

I am bit tired of getting -3 IMPs for every cold game my opponents bid and make (and no, getting +3 IMPs for every cold game we bid and make does not make up for that, the whole point is minimizing the effect of who holds better cards). I understand that 16 scores as max for comparing is hardcoded, but why dont you do what every Butler IMPs pairs game does and simply disregard extreme scores when calculating averages (say 3 extremes from each side). Thats surely not hardcoded.

[Mbodell]

Throwing out data will result in worse results overall. All data should be valid. The right fix is to compare with more than 16 other tables, which is possible in tournaments, if not in normal play.

[gwnn]

The problem would not be solved by throwing out a few results. The problem could only be solved by teaching the whole field better bidding and play, something that for understandable reasons BBO does not endeavour at this moment.

[Gerardo]

BBO uses cross imps, not butler.

 

The metho to obtain the result is very similar as how matchpoints are calculated, replacing the 1/0.5/0 result by the difference according to IMP table and (optionally; BBO does it) divide by the number of comparisons..

 

A recent thread went about the advantages of this vs butler.

 

IMO, the only advantage of butler is needing fewer calculations to obtain a result, and when you use a computer that point is moot.

[brian_m]

BBO uses cross imps, not butler.

 

The metho to obtain the result is very similar as how matchpoints are calculated, replacing the 1/0.5/0 result by the difference according to IMP table and (optionally; BBO does it) divide by the number of comparisons..

 

A recent thread went about the advantages of this vs butler.

 

IMO, the only advantage of butler is needing fewer calculations to obtain a result, and when you use a computer that point is moot.

 

 

Sixteen does seem an unreasonably low number of comparisons, though. In the days when I was an OKBridge member, with a MUCH lower total membership than BBO, they still managed to use fifty plays per board.

 

Going back to the OP's point, I'm not so much bothered about exchanging a couple of IMPs for cold games as I am about the morons who give (and accept) impossible results, just because one side landed in a ridiculous contract. THAT is really frustrating, particularly when the board has had only a few plays when you get to it. Yes, I know the scores will even out as the board has further plays, but it still skews the running score. Over nearly 40 years of playing bridge I've screwed up hands in almost every way imaginable, but I've yet to find any way to avoid making at least four tricks when I have AKQJ of trumps in my hand.

[barmar]

Since OKbridge calculates Lehmans, while BBO doesn't, one could argue that the number of comparisons is more important on OKb.

 

While those ridiculous scores can be annoying, how many of the boards you play in a session actually have them? If you play a couple dozen boards, and one of them had a joker on it, this shouldn't have a big effect on your total.

[gwnn]

barmar, zenko is right that if you sit down in the main bridge club, bid and make 3NT on 26 HCP with 8 top tricks plus a finesse, you're likely to get 2-3 imps, because some people miss game and some others go down for some reason. If you bid and make a game you have a good solid + EV on BBO, something that is slightly annoying (personally I do not get annoyed by this but I understand people who do). However, just discarding a few results will not do it. You would need to teach people to take finesses and take their top tricks, something that is beyond the scope of score calculation.

[brian_m]

Since OKbridge calculates Lehmans, while BBO doesn't, one could argue that the number of comparisons is more important on OKb.

 

While those ridiculous scores can be annoying, how many of the boards you play in a session actually have them? If you play a couple dozen boards, and one of them had a joker on it, this shouldn't have a big effect on your total.

 

I realise OKB had the additional motivation for the larger number of comparisons, but it still seems to me that sixteen is a bit low.

 

And sure, the ridiculous scores don't occur that often. I'd put it a little higher than you do, not the downright impossible scores but the ludicrous contracts (e.g. one member of a partnership is playing strong twos, the other weak, and in amongst all the slams and games you have a 2H+4).

 

I can see the case for winding up the number of plays and discarding the top and bottom, but then I don't have to implement it.

[semeai]

Throwing out say one extreme result on each end in the cross imps wouldn't help with the 3 imps/game problem, but it would negate the 7ntxx-6 style of scores.

 

For the 3 imp/game problem, you have to do something different. Some ideas:

 

1) Play a team match

 

2) Maybe BBO could implement "compare this table vs 4 GIB's" for people who've paid for GIB for that day/week? Can this already be done? This may be better, but would have its own annoyances too.

 

3) Maybe BBO could implement "compare this table vs par"? This would be interesting, but would again have its own annoyances such as when the other table bids and makes a slam requiring three finesses and a squeeze.

[BunnyGo]

An idea I proposed before is to just compare to par. This is clearly rough when a DD 22 pt slam makes (or some other such extreme example), but it is probably less annoying than comparing with 5 tables that don't know how to play, 5 tables that judged to stay out of game and 5 tables that you push with.

[Bbradley62]

The problem would not be solved by throwing out a few results. The problem could only be solved by teaching the whole field better bidding and play, something that for understandable reasons BBO does not endeavour at this moment.

It's probably anti-BBO-philosophy, but one way to combat this might be to create an Advanced Bridge Club, that players have to qualify (in some way, shape or form) to play in.

[hotShot]

The 16 Board limit was introduces when BBO still was very small (less than 100 player online) and it took ages to complete a board.

The limit was hard coded into the Windows-Client and and that limit propagated into the server software.

One day the support of the Windows-Client might end and after that the 16 score limit will hopefully be history.

[brian_m]

The 16 Board limit was introduces when BBO still was very small (less than 100 player online) and it took ages to complete a board.

The limit was hard coded into the Windows-Client and and that limit propagated into the server software.

One day the support of the Windows-Client might end and after that the 16 score limit will hopefully be history.

 

As a user of the Windows client, albeit under Linux, I certainly hope that day is a long way away. I've tried the web client and I detest the interface.

 

As a (retired) database programmer myself, I would be surprised to learn that something like that had been hard-coded in such a way that increasing it would require significant amounts of work. Yes, there are limits that you can't get round, e.g. the self-contained database code with which I was most familiar limited you to 1,000,000 records per table and a record size of 32,000 bytes, but I've never heard of a toolbox that would be responsible for a limit of 16 plays.

[zenko]

All I am askng for is scoring method that will corelate with quality of my effort, is that really too much to ask?

 

For those who do not like Butler socring here are few clarifications:

 

1) Nothing gets "thrown out", extremes are just not counted when calculating the average, ALL results are then compared to that "normalized" average.

 

2) Disregarding 3 results from each side would help a lot to reduce that 3 IMPs per board "declarer advantage". If you examine typical cold game score sheet "funny" results are almost never equally distributed at the both ends, usually you have about 3-5 on one side (missed/failed game, tried slam) and 1-3 in the other (contract doubled and made), using middle 10 results would help a lot.

 

3) Team matches are even more volatile, even if all 8 players are competent, becuase there is only one comparising, playng against "the field" is much better to figure out where is your game

 

4)"it all evens out anyway" just makes no sense. For start it is quite common that you play set of 20-30 boards that is very onesided result-wise, so yes it all evens out in very long run, but who cares? In the long run we are all dead too.

 

And one more thing: being involved in lot of software development (yes in Flex/Flash environment too!) I can not shake off the feeling that there is simply not much going on lately at BBO Inc. on that front. If the money is the issue I suggest doing some kind of drive like Wikipedia does, I am the first one who will donate some money if it means hiring an additional programer to help Uday, if it would lead to better user experience.

[barmar]

1) Nothing gets "thrown out", extremes are just not counted when calculating the average, ALL results are then compared to that "normalized" average.

We don't compare to an average, we do cross-IMP scoring. Comparing to an average was mainly done in the days of hand scoring, because it required fewer calculations. Cross-IMP is most common with computer scoring.

[zenko]

We don't compare to an average, we do cross-IMP scoring. Comparing to an average was mainly done in the days of hand scoring, because it required fewer calculations. Cross-IMP is most common with computer scoring.

 

 

No it was not done to reduce number of calculations, it is done to reduce disparity of median and mean results, actually it is even more important to do it with less than statistcally significant number of results to compare, becuse a few freak results will throw the mean completely out of whack.

[gwnn]

No it was not done to reduce number of calculations, it is done to reduce disparity of median and mean results, actually it is even more important to do it with less than statistcally significant number of results to compare, becuse a few freak results will throw the mean completely out of whack.

It was too.

 

Comparing to an average value like -235 will yield unbridge-like imp results (results that the imp table was not designed for).

[brian_m]

It was too.

 

Comparing to an average value like -235 will yield unbridge-like imp results (results that the imp table was not designed for).

 

Having hand-scored more than my fair share of Butlers, all you do is round the calculated average before comparing. What's the problem? One line of code if you're doing it with a program.

[gwnn]

The imp table is designed around common bridge swings such as 480 vs 980, 170 vs 620 etc. It is not designed around swings like 480 vs 730. It is a subtle problem but a relevant one (and not one I came up witg).

[matmat]

Here's a novel idea. Stop trying to use your BBO IMP scores to gauge how good you are at bridge.

[brian_m]

Here's a novel idea. Stop trying to use your BBO IMP scores to gauge how good you are at bridge.

 

Maybe I'm the only one in this thread who plays in a regular game (though I very much doubt it). The IMP score is a simple way to come up with some kind of measure as to who's got the better of a 20-30 board session amongst players of comparable strengths. Why does wanting to minimise the distortions caused by the idiotic results imply anything about trying to assess "how good we are at bridge"?

 

Here's a novel idea for you. Stop trying to be a smartarse.

[matmat]

Maybe I'm the only one in this thread who plays in a regular game (though I very much doubt it). The IMP score is a simple way to come up with some kind of measure as to who's got the better of a 20-30 board session amongst players of comparable strengths. Why does wanting to minimise the distortions caused by the idiotic results imply anything about trying to assess "how good we are at bridge"?

 

Here's a novel idea for you. Stop trying to be a smartarse.

so who gets to decide what is an idiotic result and what isn't? is one pair in 16 making a slam they bid on a favorable lead idiotic if the rest of the field is taking the same number of tricks in game? is a couple of players making 3n on an exotic squeeze when the rest of the field is off idiotic? who are you to judge? If you have a set game, perhaps it wouldn't be that much more of an effort to set up a set team match, then you really don't have to worry about the rest of the bbo field.

[brian_m]

so who gets to decide what is an idiotic result and what isn't? is one pair in 16 making a slam they bid on a favorable lead idiotic if the rest of the field is taking the same number of tricks in game? is a couple of players making 3n on an exotic squeeze when the rest of the field is off idiotic? who are you to judge? If you have a set game, perhaps it wouldn't be that much more of an effort to set up a set team match, then you really don't have to worry about the rest of the bbo field.

 

I didn't say anyone should decide what was an idiotic result, and certainly not that I should do it. I just noted their existence.

 

If you look back through the thread, and perhaps read a little more carefully, you'll see that my suggestion is that the number of plays of each board be increased, and then the top and bottom result be disregarded. There would need to be a little more thought put into this - the pairs concerned still keeping their scores, but their scores being disregarded for cross-imping the rest of the board (although I can't honestly see a problem with a Butler-type calculation).

 

And no, I'm not saying that one pair getting into a massively anti-percentage slam and then making on a lucky lead is an idiotic result. Lucky, yes, idiotic, no. What I'm calling an idiotic result is those in the 7NT**-7 sort of category. Perhaps boards where a pair goes down more than three tricks redoubled should be automatically flagged for review, to see whether the pairs concerned are just playing silly buggers.

 

And so another straw man is (hopefully!) laid to rest...

 

As regards your suggestion of playing team games - they're rather difficult to arrange with only four regulars, but if there are another four players reading this who play a set game starting around 7pm New Zealand time, I'm more than happy to try to set something up, please send me a private message.

[fred]

The 16 Board limit was introduces when BBO still was very small (less than 100 player online) and it took ages to complete a board.

The limit was hard coded into the Windows-Client and and that limit propagated into the server software.

One day the support of the Windows-Client might end and after that the 16 score limit will hopefully be history.

That is correct. The Windows client cannot handle more than 16 plays per board and that is not going to change. Our server software also has some hardcoded assumptions about 16 boards, both it would be relatively easy to change that.

 

It is possible that we will eventually open a new area on BBO for web-client users only with various features (like more than 16 plays per board) that are not supported in the Windows client.

 

Although we are not planning on changing or improving the Windows client, we have no plans to force people to stop using it. Our plan is to continue to improve the web-client with the expectation that more and more BBO members will continue to migrate.

 

I very much doubt that we will change the way we score boards. If we ever do, such change(s) will take effect for web-client users only.

 

Fred Gitelman

Bridge Base Inc.

www.bridgebase.com

[xarlos]

Throwing out data will result in worse results overall. All data should be valid. The right fix is to compare with more than 16 other tables, which is possible in tournaments, if not in normal play.

 

I disagree. Throwing out extreme data (2sd+ from the mean) will result in regression to the mean.