The SeeSaw Effect

Hi Michael,

Today we played the Hesitation Mitchell movement at the club ..... and if you look at our results you will see the winner got a whopping 82% ...... if you look at most of our members playing – the ones sitting N/S got bigger percentages with X Clubs and the E/W had their percentages dropped considerably with X Clubs. How could this have happened do you think? It seems so strange.

Not at all - it's usual. In fact.

When your club results are scored across a larger field you can bank on one thing: neither of your N/S or E/W players will have done exactly the same as all the other N/S or E/W fields involved. One will be scored higher ... maybe even by as much as 10% ... and the other lower by a corresponding amount. It's what I have christened the SeeSaw Effect - in the bigger field each side, too, must average out at 50%. Them's that go UP must be balanced by others that go DOWN. So in one club it might happen that the N/S scores will average 54% after scoring across - then the E/W's in that club session will average 46%. In some other club the E/W's will go up and the N/S's will go down to balance this out. It's a mathematical certainty dictated by the intrinsic ramifications of matchpoint scoring.

Michael

PS - See also http://www.compassmate.bridge-centre.org/nzw04 which deduces that it takes about 120 pairs before the statistical relevance of a result can be nailed to within ±0.5%. You might also read http://www.compassmate.bridge-centre.org/karen01