Monday, February 15, 2010

A den of iniquity?

Oh the iniquities (or should that be inequities) of the ACBL matchpoint scoring system!  I've been thinking for a long while now how silly it is that placings can often be decided by fractions of a matchpoint.

Because a table in Saturday's A/X pairs at Cromwell managed to report a strange result on a board (one pair was given a "no-play"), the factoring process kicked in for that one board.  This robbed Peter Matthews and I of a 2nd place tie and a whopping 2.2 masterpoints!  On the board in question, we were +100 for 7.63 matchpoints.  Our rivals were +80 for 4.92.  In other words, on that board we beat them by 2.71 mps.  For the other 51 boards, their score was 352.5 while ours was 349.5 mps.

Now, let's look at the effect of the various scores at the other table on this board:

scoretheir mps our mps their total our total our position
50 or lower5.58358357.53rd
8058357.5357.5tied 2/3
1004.57.5357357tied 2/3
110 or higher4.57357356.53rd

So in two out of three scenarios, we would be third, in one scenario would we be second, while in the other two scenarios, we would be tied.  But when it is so close, why don't they simply admit that the two pairs can't be reliably separated and call them both 2nd equal?  Then they could split the masterpoint awards by an appropriate ratio.  The awards in this case were 17.59 for 2nd place and 13.19 for 3rd place.  If there was a dead tie, each pair would get 15.39 points.  A more equitable sharing of masterpoint awards for the circumstances described here would be 15.83 and 14.95 (this assumes, rather arbitrarily, that all five scenarios are equally likely).

In actual fact, we do know the result at the other table because the pair sitting in the opposite direction were credited with -100.  Had that result stood for both pairs at the table, we would have been tied for second.  I don't know why the pair in our direction was given a no-play but presumably they were somehow damaged by the events at the table in a way that couldn't be redressed.  At the same time, their opponents were given the table result which was, for them, below average (37.5%).  And by the way, the pair that got the "NP" result were well out of the money and so any result for them would have made no difference at all.

Ah well, it's the bridge that's the thing, not the masterpoints!  Who cares about masterpoints?  But it does seem silly that placings should be determined by such uncertainties.

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