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To Switch or not to Switch ?

We asked our Tournament Director, Mike Amos, to explain why it is entirely a club decision as to whether a Mitchell movement should have an arrow switch at the club when playing our Simultaneous Pairs. He says:

A completed Mitchell movement with no half tables provides a perfect competition for the two lines NS and EW - they all play the same boards and the same opponents - the comparison is completely fair and is effectively two competitions with two winners.

However if for some reason a single winner is required, it now becomes effectively one competition and not two so things are not so easy.

Imagine a competition in which every NS pair were clones of Boris Schapiro and Terrence Reese and EW were clowns of Mike Amos and Anna Gudge. At the end of the evening one of the Boris/Terrence pairs would have scored 38% and one of the Amos/Gudge pairs 62% but there would be no real comparison between the two sets of scores. Why ? Because we have played different cards and different opponents.

Imagine that we are a NS pair at table 1. In Round 1 we play against EW1. All of the match points are at stake and they are our enemy - the better they bid and play or defend, the poorer our score and the better they do. But we also have other enemies on Board 1 because when it is played at Table 2 the NS pair there are our opponents. If they do better than us then they reduce our Match Point score by two. Moreover, the EW opponents of NS 2 are our allies because if they do well the NS pair will do poorly and so our score will be improved ... and so it is on every single board throughout the evening. We have allies who help us and enemies who can reduce our score - once EW 1 leave our table they will become our allies on every other single board of the competition so we should wish them well as they go round the room!

Now in a standard Mitchell movement the balance betwen allies and enemies is not quite right - more matchpoints are at stake against those who sit the same way as we do than against the opposing line. Arrow-switching redresses this balance. Theoretically it should apply to around 1/8 of the boards but in practice we do not fiddle around too much - it is normal to arrowswitch once in 7, 8, 9, 10 or 11 rounds and twice in longer movements - many 3/4 Howell movements have arrowswitches which are designed to achieve the same thing - a better comparison and balance between all players.

BALANCE is the key word - it achieves a balance between comparisons among fellow competitors in terms of allies and opponents.

So ... if you want to know who has performed best in your club on a single evening session you should arrow switch. But, as far as a simultaneous paris is comcerned, this is entirely fruitless. The issue of balance is irrelevant - you are only playing a tiny fraction of the competitors and once comparisons start to be made with other clubs huge changes in the scores occur anyway. An EW pair who score 60% in their club may find this increases to 70% or maybe more if the NS scores in their club are poor, and the reverse can happen of course - a 60% local score can decline to 50% or even less. All that arrowswitching will do will be to randomise these variations. There is no real point because the national ranking will provide a good indicator of the best club performance on the night. Arrow-switching will just give the poor TD and scorers one extra chance to make an error(Not to mention the players who forget and so on...)

In conclusion - Arrowswitching is essential to provide a single winner in a session but irrelevant in the context of a simultaneous pairs.

Why do the Scores change?