[savphantom]

Using X-Imp Pairs competition to select Pairs for representative team and problem occurred with much discussion.
What adjustments to scoring should be employed to deal with a fouled board(removed from 1 Match) or curtailment because of withdrawal because of illness
when no substitute is available or allowed to play several boards to complete a match. View is that +2 IMP for average plus is a windfall for three or four boards not played.
Generally elimination stages would involve 10 pairs, playing full Howell type movement over 3 or so sessions and matches of 16 to 20 boards.
In Australia where common to use VP scoring WBF Scales 0-25 VP.

[campboy]

It's a matter of local regulation. FWIW the EBU regulation is +2 IMPs. The problem of ave+ for several boards being too high applies for any form of scoring, of course, but I don't think many places have a different regulation for that case (yet).

[Trinidad]

Campboy is correct: It is a matter of regulation and most regulators chose to make +/- 2 IMP the equivalent of 60/40%. There has also been some empirical research comparing scores in MP pairs and XIMP pairs tournaments leading to the conclusion that 60% is equivalent to a little below 2 XIMP. Therefore, these regulations seem to be spot on.

A XIMP tournament has the interesting feature that for a small number of tables it converges to an actual team of 4 match. When you score a team of 4 match as XIMP for the individual pairs you will obtain the team score whe you add the XIMP score from NS at table 1 to that of EW at table 2. Since these will be equal, you can say that the team score equals 2x the pair score (which makes sense, since the team consists of 2 pairs).

If, for some reason, a score is impossible in a team of four match, the teams will be awarded +/- 3 IMPs. Or, each pair will get +/- 1.5 IMP. From that point of view, it would be better to make +/- 1.5 XIMP the equivalent of 60-40%.

Am I arguing in favor of regulations that award +/- 1.5 XIMP as the equivalent of 60-40%? Not really. I think the empirical data are pretty powerful. However, I think this is an argument for changing the law on team of four matches in such a way that the equivalent of 60-40% is 4 IMPs, rather than 3 IMPs as it is now. The basis for this is the mathematics of XIMPs (converging to team of four) and the empirical data that are available now (but weren't when the decision for 3 IMPs was made).

Rik

[savphantom]

Thanks for the thoughts;
The local strong critic of +/- 2 IMP argues on the line that
"For 20 board match our Max Win is 34.1 IMPS with 1 IMP = 1 VP so
34.1 is 50% above the average result of 0 so Average+ or 10% above average should be 6.82 IMp thus the adjustment for 1 board is 6.82/20 or 0.341 VP per board."

Not being a serious maths or statistics man I suspect averaging a result from 20 boards is not relevant to the value of 1 or 2 boards cancelled where you lose all chance of playing well or being lucky.
Also hard to believe the authorities such as WBFLC have got it all wrong for so long.

[mgoetze]

savphantom, on 2011-June-02, 18:53, said:

Not being a serious maths or statistics man I suspect averaging a result from 20 boards is not relevant to the value of 1 or 2 boards cancelled where you lose all chance of playing well or being lucky.

I suppose the point is, as the number of boards increases, the variance decreases, and thus it would not be unreasonable, when awarding average plus for 20 boards, to award less per board than when doing so for only 1 or 2 boards.