Teams of Eight
EBU Score allows four different methods of scoring teams of eight.
Two Teams of 4 Imp-ed and added, X-Imps, Aggregate (two options).
I know (from somewhere) that the Aggregate options are not favoured by the EBU.
But can someone tell me the pros and cons of each method?
Comments
The best is the cross-IMP method, because it uses all combinations of all scores, but it's also the most complicated to score without a scoring program, so tends just to be used for serious events.
The add then IMP method is simple to do, but it's using a scale that was not designed for this purpose and will give results that are effectively compressed, so good results are insufficiently rewarded. Using this method with the Modified IMP scale attempts to address this shortcoming and is a reasonable compromise if you want the simplicity of just adding all four scores.
Scoring as two teams of four is also a reasonable method, but it does have the effect that it may make a difference who you are paired with as to how well you score as a team.
The XIMP method also is affected by the difference of 'who you are paired with' (or at least, who you are NOT paired with).
In two teams of four, you lose out (e.g.) if you and your team-mates get good results on the same board, by comparison to the score you would have got if a pair from each team-of-four get a good result on the same board, or indeed if two pairs get good results on different boards.
In XIMPs, you lose out if, on the same board, one EW & one NS both get good results (by comparison to the score you would get if both NS's got a good result).
I studied this a while ago, with a very simplistic model, and concluded that there wasn't much difference in the fairness. But XIMPs certainly 'feels like' the better method, and a more serious study might back this up.
You might observe that using the 'aggregate' method, if you have two pairs getting good results on the same board, it doesn't matter which polarities they are in! In this case, you will get a poorer result, regardless, than the effect of those two pairs having achieved a better result on separate boards.
White Book 3.7.1 is probably where you saw it. The method is, nevertheless, still used by the counties near me in their County Leagues of teams of eight, and that's likely because it is the easiest method when scoring manually, despite the disadvantages discussed above.
Barrie Partridge - CTD for Bridge Club Live