SuitPlay Help

Compare lines

There are various ways to compare lines of play. If you just want to know which line has the highest probability for 3 tricks, say, then you can look in the Strat x Goal table. You can find this table under Analysis in the menu. There you find probabilities for all lines and all goals.

There exists a new and better method of comparing lines of play. This method takes into account the form of scoring: matchpoints or imps. The method has been described in The Bridge World and other magazines.

Matchpoints

When comparing two lines of play at matchpoints, it only matters how often one line wins over the other, and how often it loses. It does not matter by how many tricks one line wins over the other. One line is better than another line if it wins more often than it loses. The "mp-best" line determined by SuitPlay wins more often than it loses when it is compared with any other possible line of play for the specified suit combination. You can find "mp-best" in the Result table in the main form.

As an example, consider
North:A Q 10 9 8
South:5 4 3 2

The line that gives the most tricks on average is A: "small to the queen". However, with matchpoint scoring, line C "small to the ten" is better! Line A gains when West-East hold Kx-Jx or Kxx-J, just below 20% (*). Line C gains when West-East hold KJxx-, KJx-x or Jxx-K. This chance is over 23% (**). The conclusion is that line C wins more often from line A than vice versa, so line C is better. The fact that A sometimes gains two tricks is irrelevant for matchpoint scoring. In the Strat x Goal table you can find that C wins from A (first row, last column). Line C loses from no other line (last row, last column is empty), so C is "mp-best" You can find the difference between (**) and (*) in the Pay-off table, under "Analysis" in the menu. In the example, the difference is 3,6522% in favor of C.

IMPS

When comparing two lines of play at imp scoring, SuitPlay computes the expected number of imps per deals one line wins over the other. One line of play is better than another when the expected number of imps it wins is greater than the expected number of imps it loses. The "imp-best" line of play determined by SuitPlay is better than any other possible line of play for the specified suit combination.

By default, SuitPlay uses matchpoint comparison and hence "mp-best". You will obtain "imp-best" when you enter the suit combination and select the fourth advanced option.

Here is an example:
North:Q 5 4 3
South:A 10 2
The contract is 3NT vulnerable and two tricks are needed in this suit to make the contract.

The results give three lines of play. Line B is the best line to secure the contract (goal = 2). But line C is imp-best, according to SuitPlay. So let us compare line B with C. In the Tricks table one can see that B wins one overtrick imp in the following case
West-Eastprob.B C
KJ-xxxx 1.61%3 2
and line B makes 3NT (600 points) where C goes down (-100) in the following case:
West-Eastprob.B C
J-Kxxxx 1.21%2 1
This difference is worth 12 imps.

So line B expects to win
1.21%*12imps+
1.61%*1 imp = 0.1614
imps per deal over C.

However, line C wins an overtrick imp in the following cases:
West-Eastprob.B C
Kxx-Jxx10.66%2 3
xxx-KJx 7.11%2 3
---------
17.77%

So line C wins 0.1777 imps per deal on average over B. Since 0.1777 is more than 0.1614, the conclusion is that C is the winner. The difference between these numbers can be found in the pay-off table.

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Last revised: 07/10/2010