International Matchpoint Scale

In this column, we will focus on why it pays to be aggressive when bidding games at IMPs. We will also consider small slam and grand slam bidding. For your convenience, here is the IMP scale.

Diff. in Pts. IMPs Diff. in Pts. IMPs Diff. in Pts. IMPs Diff. in Pts. IMPs

20-40 ………..1 270-310 …..……7 750-890 ……..13 2000-2240 …..19

50-80 ….…….2 320-360 …..……8 900-1090 ……14 2250-2490 …..20

90-120 ………3 370-420 ….…….9 1100-1290 …..15 2500-2990 …..21

130-160 ……..4 430-490 ………10 1300-1490 …..16 3000-3490 …..22

170-210 ……..5 500-590 ………11 1500-1740 …..17 3500-3990 …..23

220-260 ……..6 600-740 ………12 1750-1990 …..18 4000 and up …24

You are playing in a team game, and your partner makes a game invitation. For simplicity’s sake, we will assume a spade contract – the analysis is almost identical for NT or minor suits. What should dictate our decision?

Let’s assume for the moment that there are two possible outcomes – making three or making four. Let’s further assume that the opponents have stopped in three. Let’s see what happens if we bid the game.

Our side Non-Vulnerable	Contract only makes nine tricks	Contract makes ten tricks
Our score	-50	+420
Our partners score	-140	-170
Net total points	-190	+250
IMPS	-5	+6

In this scenario, if the game makes, we gain six IMPs by bidding game. If game goes down, we lose five IMPs. You can clearly see that if we bid all games that are even money to make, we would gain more IMPs than we lose. We actually need to be bidding games that may be a slight underdog, as well still can come out ahead if they make. The actual breakeven point is bidding all games that have at least a 45.5% (5/11 for you math majors out there) chance of making. Let’s look at the scenario if our side is vulnerable.

Our side Vulnerable	Contract only makes nine tricks	Contract makes ten tricks
Our score	-100	+620
Our partners score	-140	-170
Net total points	-240	+450
IMPS	-6	+10

If the vulnerable game makes, we gain ten IMPs by bidding. If the game goes down, we only lose 6 IMPs. Interestingly, it pays to be even more aggressive vulnerable than non vulnerable. You should strive to bid all games with at least a 37.5% (6/16) chance of making.

Let’s use a similar analysis for bidding a small slam. We will again only two possible outcome, making five or six. We will also assume that the opponents did not bid the slam. Here is the corresponding analysis:

Our side Non-Vulnerable	Contract only makes eleven tricks	Contract makes twelve tricks
Our score	-50	+980
Our partners score	-450	-480
Net total points	-500	+500
IMPS	-11	+11

Our side Vulnerable	Contract only makes eleven tricks	Contract makes twelve tricks
Our score	-100	+1430
Our partners score	-650	-680
Net total points	-750	+750
IMPS	-13	+13

Interestingly, for slam bidding, the risk of missing slam, and the reward for bidding are identical. Thus, you should aim to bid all slams that are 50% or better, and avoid inferior slams. Stretching to a small slam is not a winning strategy. Note that this is true at any vulnerability.

Let’s look at grand slams. Again, I am only considering making six and making seven. The opponents have bid a small slam. We are bidding a grand slam:

Our side Non-Vulnerable	Contract only makes twelve tricks	Contract makes thirteen tricks
Our score	-50	+1510
Our partners score	-980	-1010
Net total points	-1030	+500
IMPS	-14	+11

You stand to lose more by being wrong, than you gain by bidding on. Therefore, you should not bid a grand slam unless the contract has at least a 56% chance of success non-vulnerable. Let’s look at a vulnerable grand slam:

Our side Vulnerable	Contract only makes twelve tricks	Contract makes thirteen tricks
Our score	-100	+2220
Our partners score	-1430	-1460
Net total points	-1530	+750
IMPS	-17	+13

For grand slams, vulnerability matters a bit. Surprisingly, you need to be more conservative vulnerable than not, when it come to grand slams. Don’t bid a vulnerable grand unless the contract has a 57% chance of success.

I have left one thing out of the grand slam analysis, and this is important. Have you ever bid an unsuccessful grand slam, and later found out that the opponents did not even bid a small slam? This is a painful discussion to have with your partners. This is another way that bidding thin grand slams can hurt you.

To summarize our discussion, bid games aggressively at IMPS, especially when vulnerable. Bidding a 50% small slam (e.g. on a finesse) is a breakeven proposition. Only bid grand slams that are a favorite to make.

In the next issue, we will look at IMP strategy for bidding partscores.