EBU National Grading Scheme

[gnasher]

You are right about multiple teams and Swiss events. I think it is desirable to include the head to head matches but there has to be some thought about how it gets recorded. If you organise a team competition and you want to get something as basic as who played and how many boards it is remarkably difficult! If something is to happen it can't rely on a load of manual data and amending data so this will need some thought first.

I don't think you need any more information than for a pairs event.

 

When you enter a pairs event, you and your partner are treated as a single contestant, and each of you gets equal credit or discredit for the result. Therefore all you need to know is (a) who the players were in each partnership and (b) what the overall score was.

 

When you enter a teams event, you and your teammates should also be treated as a single contestant. Therefore all you need to know is (a) who the players were in each team and (b) what the overall score was.

 

In a cross-IMPed pairs, each player's rank for the session is:

SGa = Ga + (6.48i/x + SOpp – Ga/2 – Gb/2)

 

In a head-to-head teams match, each player's rank should be:

SGa = Ga + (6.48i/x + SOpp – Ga/4 – Gb/4 – Gc/4 – Gd/4)

 

where

Ga = your rank

G[b-d] = partner's/teammates' rank

SOpp = strength of opposition

i = net IMPs

x = no of boards played.

[AlexJonson]

I guess the issue is 'head to head' teams of four where some teams have six players (or n), so you have to think about the consequences of that.

 

When I was young, I would have said teams of 4 should = 4 players, but that is probably impractical.

 

I doubt that it's acceptable with more than 4 without knowing who played and when, to just equalise all the results.

[Cthulhu D]

For the "strong newcomer" problem in general, I think it would be OK to make a subjective decision in a case where a new member had previously played in another country, and perhaps also where a player has reappeared after an absence of several years.

 

Alternatively, what about waiting until they'd played enough times to produce a reliable grade, then retrospectively applying that to the games they played earlier? Or are there technical obstacles to that?

 

Yeah if a superstar turns up you can probably do it by hand, the alternative is the chess solution. You make established players grades more resistant to change and new players very flexible on the basis that you have confidence that your established ratings are right. This also protects established players from damage because the adjustment from losing to someone is pretty low. This also protects established players who turn up and have a disaster session for external reasons.

[Jeremy69A]

You may be able to find a way to assess a grade from a locally played teams match but you also have to deal with the input of data into the system. For all pairs and events it is done automatically. Bridgemates in every home?

[gnasher]

You may be able to find a way to assess a grade from a locally played teams match but you also have to deal with the input of data into the system. For all pairs and events it is done automatically. Bridgemates in every home?

When I report a the result of a Crockfords match, I send an email to the EBU telling them:

- Who won.

- Who played on the winning side (assuming that it's a team of more than four).

Somehow this information makes its way into the Masterpoint system, so somebody at the EBU must type it onto a computer.

 

If they were using this information for grading, they would need to know, in addition:

- The winning score

- Who played on the losing side

 

So yes, it would create a bit more work for the EBU staff, but it's not an order-of-magnitude difference from what is currently done. Alternatively, you could provide an online form for reporting match results.

[gnasher]

Actually, thinking about this a bit more, with a head-to-head knockout match I don't see any need to know the IMP difference.

 

The objective is to win, so the players should be rated on whether they achieved that objective. Once you start rewarding them for winning heavily or penalising them for losing heavily, you create conflicting objectives.

 

When a team is behind, we want them to try to turn the match around. We really don't want to see them playing conservatively so as to limit the damage to their grade, like some mediocre cricketer batting for his average.

[Jeremy69A]

When a team is behind, we want them to try to turn the match around. We really don't want to see them playing conservatively so as to limit the damage to their grade, like some mediocre cricketer batting for his average.

 

I don't think it is the role of the grading system or its inventors to have a view about how contestants play. It will be for the contestants to decided what they think is best. If you do decide on imps etc rather than straight result you also have to think about the effect of concessions.

If you play at the club on a normal pairs night and are doing mediocrely with a few rounds to go will you try to win by edging a few over the slips or will you play for your NGS rating? I guess in those clubs with ladders this problem has had to be resolved by contestants before.

 

Actually, thinking about this a bit more, with a head-to-head knockout match I don't see any need to know the IMP difference.

 

That would simplify it.

 

I'm sure it will be possible to sort something out but the devil will be in the detail to make it as meaningful as possible without creating a significant extra workload and therefore cost

[mchristie]

Yes, we are slowly working towards using teams events, for events such as SwissTeams where the boards are played multiple times. They will be graded by looking at the performance of individual pairs.

For individual team of four matches, yes there are problems about data collection which could probably be overcome with a lot of effort, but the biggest issue is that there is only one result and it affects equally all eight players. That makes each board statistically worth only 1/4 of a dupliacte pairs board, so a 48 board match would be given as much weight as a 12 board pairs session. But..., the biggest problem is "systematic errors". The NGS suffers a bit from this, if a player is over or undergraded, this affects their partner's grade, and leads to people complaining about the system. For head to head team matches, you grade is susceptible to errors in any of the other seven players. I suspect that the inclusion of such events would simply make individual grades less reliable.

[gnasher]

the biggest issue is that there is only one result and it affects equally all eight players. That makes each board statistically worth only 1/4 of a dupliacte pairs board, so a 48 board match would be given as much weight as a 12 board pairs session.

Surely the ratio is 2:1, not 4:1? A pairs result affects two players, and a teams result affects four players, so a 48-board match is worth a 24-board pairs session.

[mchristie]

Surely the ratio is 2:1, not 4:1? A pairs result affects two players, and a teams result affects four players, so a 48-board match is worth a 24-board pairs session.

That's what I thought originally, but in a head-to-head match the four players at THE ONLY OTHER table have an equal impact on the result, so such a result affects eight players, thereby contributing a second 2:1 factor. Once a board is played at several other tables the effect of the other tables' players rapidly diminishes. I think it's (n/n-1) if the board is played n times.

[gnasher]

I don't think it is the role of the grading system or its inventors to have a view about how contestants play. It will be for the contestants to decided what they think is best. If you do decide on imps etc rather than straight result you also have to think about the effect of concessions.

Yes, concessions are another reason to grade people (in knockout matches) solely on the basis of whether they won or lost. Maybe it's worthwhile to compare it with chess: in chess they don't grade players on the basis of how many moves they took to win, or how many pieces up the winner was at the end - all that matters is the final result.

 

For similar reasons, I would grade Swiss matches according to the number of VPs won or lost and the strength of the opponents, ignoring the results on the individual boards.

 

It sounds as though I've entered this discussion rather too late, though. And of course Mike and others have put much more thought into this than I have.

Edited April 13, 2012 by gnasher

[Vampyr]

A quick question: In Swiss teams, Bridgemate II's give the names that they expect to appear at the table. Can they be programmed to switch the names to the ones that actually appeared at the table? What if there are more than 4 players on a team or the partnerships have swapped?

 

And if all this is possible, can the players be relied upon to make the changes (and make them accurately)?

[Oof Arted]

A quick question: In Swiss teams, Bridgemate II's give the names that they expect to appear at the table. Can they be programmed to switch the names to the ones that actually appeared at the table? What if there are more than 4 players on a team or the partnerships have swapped?

 

And if all this is possible, can the players be relied upon to make the changes (and make them accurately)?

 

 

:rolleyes:

 

If they know who they are possibly , but dont hold your breath B-)

[weejonnie]

Actually, currently newcomers enter on a grade of 46.00. We monitor the average performance of the approximately 100 new players joining the system per week to see what their average strangth is. Over the last few months this has been around 45-46%. If it drops any lower, we'll reduce the newcomers' ranking to match. Zia has not yet played enough rated games to get a published grade, and you may feel it was lucky for his partners to be playing with such a skillful newcomer with an initial rating of 46, but it didn't seem right to make any exceptions. Should we?

 

So this explains why the average grade for the NGS is below 49.

 

(One point - if we play in the same direction as a pair - is the SOpp the strength of the pair or the average strength of the two players?

 

I have a grade of 62.12 and a partnership grade of 59.02 with my usual partner.

 

Yet his grading is 54.87 making an average grade 58.495)

[Vampyr]

:rolleyes:

 

If they know who they are possibly , but dont hold your breath B-)

 

I think this is about right. So I really don't know how teams events can be included, unless a separate rating is created for teams. It does not seem like it will be very accurate. But maybe the brains behind the scheme will come up with something.

[Vampyr]

For the "strong newcomer" problem in general, I think it would be OK to make a subjective decision in a case where a new member had previously played in another country, and perhaps also where a player has reappeared after an absence of several years.

 

Alternatively, what about waiting until they'd played enough times to produce a reliable grade, then retrospectively applying that to the games they played earlier? Or are there technical obstacles to that?

 

I had assumed they were doing the latter, but in any case it seems obvious that it is right to do one or the other.

[gnasher]

(One point - if we play in the same direction as a pair - is the SOpp the strength of the pair or the average strength of the two players?

I'm pretty sure it's the average of the two players' grades. Apart from anything else, they don't have enough data to use partnership grades.

 

Edit: This is probably confirmed by the NGS Guide:

The strength of a field is the average current grade of all the players in an event at the start of play of that event

The guide makes a distinction between "strength of field" and "strength of opponents", but I think the intended meaning is that "strength of opponents" is also based on player-grades.

[Vampyr]

 

The guide makes a distinction between "strength of field" and "strength of opponents", but I think the intended meaning is that "strength of opponents" is also based on player-grades.

 

Apparently your grade for a session is based on the "average strength" of the field. Would it be more accurate to calculate each board against the opponents you played it against, or would this have the same end result since you are matchpointing against the field in question?

[gnasher]

Apparently your grade for a session is based on the "average strength" of the field. Would it be more accurate to calculate each board against the opponents you played it against, or would this have the same end result since you are matchpointing against the field in question?

In a two-winner Mitchell it's based on the average strength of the people who sit the same way as you do. That sounds right to me.

 

In a one-winner Mitchell (ie one with arrow-switches), it appears to be based on the average strength of the field. That also sounds right to me: if we accept that arrow-switching allows us to produce a winner by comparing the scores of the entire field, it also allows us to produce ratings by comparing against the entire field.

 

This is the relevant part of the Guide:

So the SOpp factor will vary depending on type of movement:

For Swiss Events, take the average current grade of your opponents for each match.

For 1 Winner Movements, take the average current grade of all the other pairs.

For 2 Winner Movements, take the average current grade of all the other pairs sitting in the same direction as you.

[broze]

Time for me to weigh in. I'm not going to comment too much on what I think of the accuracy of the NGS since I haven't looked through the maths too much or even got an established grade myself. However, having looked up players that I know or have partnered I was surprised at some (just some) of the ratings. The problem cases I've observed often fall into the category of player A in this example:

 

Player A and B are partners; they play together regularly and do quite well, both acquiring ratings of 57.00 or so. However, player A is completely dependent on player B and when A plays in a pickup partnership with C he does terribly, there is no "gelling" (to use the term in the NGS guide) and they almost always come in last. Player A then plays more and more with player B, getting his grade back up to 56/57 and then plays with C again with the same disastrous result.

 

The problem is player C is not a bad bridge player but only gets to play club bridge with player A. Because whenever they play together A is rated well, player C's rating suffers greatly when they do badly. Even if C manages to save a few boards and not come last, his rating still suffers unfairly because player A just can't cope with him. Is this example relevant or helpful? And with it all in mind would it not be possible for the NGS to take into account the partnership grade; i.e. the Player A - Player C grade would be so low but when they do better than their pship grade might predict this cancels out their bad results to some extent. I hope this is clear and that I haven't grossly misunderstood or overlooked something. It could be the case that the maths in place already tackles this issue in which case I haven't understood it correctly.

 

On another note, I am delighted that the EBU have instituted the NGS. I think it can only be a good thing. I am very interested in the fluctuation of my grade and may even play more bridge as a result, certainly it gives me more motivation when playing with weaker partner's to know that my good play will have a positive tangible effect even if there's no way we'll win or get into the masterpoints.

 

I hope to see the NGS develop the system further, and a few tweaks here and there wouldn't go amiss. For example, when looking down my list of sessions it would be nice for there to be a column or icon to identify the form of scoring used for a particular session, so that when a change to my grade is not registered I can ascertain the reason. Also it would be good to be able to click on a session and see the ranking of each player that played, instead of having to look them all up. Seeing as the information is easily available anyway, it seems to me that this would not be unfair or intrusive to institute (especially as people who are uncomfortable with others being able to see their ranking can opt out as I understand it).

 

Thanks to the EBU for creating this and I hope they continue to develop its use.

[barmar]

For a system like this to work well, you need lots of mixing and matching of players. The worst case is if a pair only plays together -- you can't tell how much each contributes to the partnership's results.

[Vampyr]

For a system like this to work well, you need lots of mixing and matching of players. The worst case is if a pair only plays together -- you can't tell how much each contributes to the partnership's results.

 

Yes, I have always thought that rating of pairs instead of players would be more meaningful; but anyway it is just a bit of fun.

 

There is one thing I would like to know about it; does anyone know how it works for longer events. A player with a 61% rating is expected to score 61% in a session in order to keep from dropping -- are they also expected to score 61% in a four-session event? Actually there is another thing I want to know -- in Swiss Pairs, is every match scored as a session?

[gnasher]

There is one thing I would like to know about it; does anyone know how it works for longer events. A player with a 61% rating is expected to score 61% in a session in order to keep from dropping -- are they also expected to score 61% in a four-session event?

This is discussed in the Guide, at the bottom of page 6.

 

The grade score is factored by the number of boards involved. In a multi-session event, the sessions are treated as having occurred simultaneously, on the first day of the event. Scoring 65% and 57% in two 24-board sessions will have the same effect as scoring 61% in each.

 

Actually there is another thing I want to know -- in Swiss Pairs, is every match scored as a session?

No, it's calculated as a single session. However, it shouldn't make any difference whether you treat it as one session or as seven simultaneous sessions, or even as 56 simultaneous 1-board sessions.

 

The main difference between Swiss pairs and a normal pairs is the way that the "Strength of Opponents" is calculated (explained on page 11 and summarised at the top of page 12). In a normal non-arrow-switched pairs, it's the average strengh of the pairs who sit the same way as you. In a Swiss pairs, it's the average strengh of the pairs you played against. Neither of these is perfect, because in both movements your expected result is dependent on both the people you compare with and the people you play against.

Edited October 18, 2012 by gnasher

[Vampyr]

[info]

 

Thanks.

[ash1968]

In reading this topic the one thing that stood out to me was the non-defensive attitude to the discussion from the developers of the scheme. The responses to questions raised were genuine, thoughtful and constructive. Very different from most authorities. Well done.

 

Cheers, Stephen