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Better Preempts II: Vulnerability
 
Preemption is a form of gambling. By preempting, you intentionally risk a negative score in your contract in exchange for a chance to earn a positive score when your opponents misjudge. Vulnerability, both yours and theirs, affects that gamble.
 
The traditional advice is embodied in the "Rule of 2 and 3." The rule states that when NV versus Vul, since you can afford to go down 3 doubled against an opposing game, preempts should be within 3 tricks of the level of the bid. At equal vulnerability, since you can only afford to go down 2, a preempt should be one trick more sound. Modern experts believe this advice is too conservative.  
 
South
KQJxxxx
x
xx
xxx
W
N
E
S
?
By the rule of 2 and 3, this is an acceptable 3 preempt only at favorable. However, no expert would give serious thought to not preempting 3 at equal vulnerability. 
 
South
x
xx
QJ10xxxx
xxx
W
N
E
S
P
P
?
By the rule of 2 and 3, this 5-trick hand is not worth a preempt at any colors. But anyone who passes this hand NV in third seat is seriously under-preempting. 
 
The Rule of 2 and 3 may be good enough for beginners, but it is a blunt instrument for aspiring tournament players. The rule focuses on one factor--keeping numbers smaller than the value of an opposing game, while ignoring more important considerations. If you follow the rule carefully, you will be taking risks that are too large in some situations, while not taking enough risks in others. To develop an expert understanding of preemption, you must look much deeper.
  

Vulnerability

Vulnerability has two effects on raw score. It increases:
  • The penalty when our contract fails
  • The bonus when our game or slam makes
Both effects drive us to preempt more conservatively when vulnerable. The first notion is easy to understand--if our penalties are larger, IMP losses will be larger when we go for a number. But why should an increased game bonus also make us want to preempt less often?
 
When you preempt, you make constructive bidding more difficult for both sides. If the hand belongs to you, your partnership is much more likely to misbid after a preempt than after a pass. Don't believe me? Consider these hands. They are easy to bid to the best spot using an uninterrupted constructive auction.
  
North
x
xx
AQJxxxx
xxx
South
J109x
AQx
Kx
Axxx
W
N
E
S
P
P
1
P
1
P
1NT
P
3
P
3NT
 
North
x
xx
Qxxxxxx
Qxx
South
J109x
AQx
Kx
Axxx
W
N
E
S
P
P
1
P
1
P
1NT
P
2
P
P
P
 
But what happens if North opens both hands with a preemptive 3? Partner will have a terrible guess when to bid 3NT and he is certain to go wrong some of the time.
 
South
J109x
AQx
Kx
Axxx
W
N
E
S
3
P
?
   
When we preempt, we accept two major risks--the risk of a large penalty in our contract and the risk of missing a game. Surprisingly, the risk of missing a game is a bigger consideration than going for a number! Numbers don't occur often. But if partner is an unpassed hand, preempts can lead to missed games, especially when the preemptive style allows a wide range of values and shapes. Since missed games cost us 10 IMPs apiece when we are Vul and only 6 when we are NV, the increased game bonus is a strong incentive to preempt more cautiously when Vul than when NV.
 
How can we reduce the missed-game price tag? When we are Vul and partner is an unpassed hand, restrict preempts to hands with the correct length and good suits. Missing a good game will be expensive, so tailor your preempts so that partner can easily judge when to raise your preempt to game. Wild and undisciplined preempts are for NV situations when the cost of missing game is low or for when partner is a passed hand, so that a missed game is unlikely. 
 
 
Their Vulnerability
Their vulnerability also has a strong effect on the decision to preempt. It affects:
  • The penalty when they go down
  • The number of tricks we can go down and still outscore their game
When we preempt, sometimes we push the opponents into failing contracts, even disastrously failing contracts. We will win more IMPs on those hands if the opponents are vulnerable when it happens. When they guess wrongly to defend instead of declare, we will win more/lose fewer IMPs if their game/slam is vulnerable.
 
However, there is one important note that tempers our enthusiasm. If the opponents cannot make a game, then the increased bonuses are irrelevant. An NV or Vul partscore is worth exactly the same to them. So preemption is equally unattractive against Vul and NV opponents when they only make a partscore. How can we know if they can make game? We can't know for sure of course, but when we hold significant outside defense, enough to think they can't bid a game, their vulnerability is no longer as big an incentive to preempt. 
 
Which is more important, our vulnerability or theirs? Our vulnerability slows us down every time we are vulnerable. Their vulnerability helps us only when they are vulnerable and they have a game or slam. So their vulnerability helps less often than ours hurts.
 
 
The Vulnerability Traffic Light
 
When considering a preempt, I rate preemptive opportunities by the traffic-light scale: 
 
Green Light:    NV on Vul
 
Green Light:   NV on NV
 
Yellow Light:  Vul on Vul
 
Red Light:       Vul on NV
 
The best time to preempt is NV on Vul, and the worst time is Vul on NV--that much is clear. Why should NV on NV be a better opportunity for preemption than Vul on Vul? In both cases, a down 2 sacrifice against a game will win 3-4 IMPs so they are seemingly equal.  But NV on NV is superior because a bad sacrifice against a game is not the only way to lose. A preempt could cause us to miss a game or to go down (possibly doubled) when opponents can only make a part-score. In either case, the damage will be far worse when we are vulnerable.
  • If we miss a game, it costs 10 IMPs when we are Vul and only 6 IMPs when NV 
  • If they can only make a partial, our penalty is much higher when Vul
When you consider all the ways a preempt could go wrong, it becomes clear why NV preempts are so much more attractive than Vul ones.
 
Notice how the traffic light differs from the rule of 2 and 3. Using the traffic light we treat NV on NV as an opportunity for aggressive preemption, even though it is an equal vulnerability.
 
 
Digesting This Information
To summarize, there are two ways to fail by preempting--we could miss a game or give up a number. Both cost more when we are vulnerable. When partner is a passed hand, one of those scenarios (missing a game) is no longer likely. Using these observations, we can put our advice about preemption style into this grid.
 
  We Are Vulnerable We Are Not Vulnerable
Partner is Unpassed Conservative Aggressive
Partner is Passed Aggressive Super-Aggressive
 
When we are vul and partner is unpassed, we must be conservative. We can lose by missing a game or by giving up a number, and IMP losses will tend to be larger.
 
When we are NV and partner is unpassed hand, we can be aggressive because IMP losses for missing game or a number will be smaller than the first case.
 
When we are Vul and partner is a passed hand, we can be aggressive. We have only one way to lose (a number) instead of two.
 
When we are NV and partner is a passed hand, we can be super-aggressive. We have only one way to lose and the losses will be smaller.
 
But what do these vague terms conservative, aggressive and super-aggressive mean? To some degree, that is up to you. If we wanted to translate them into rule of 2 and 3 terms, we could say:
  • Conservative = within 2 tricks of your contract
  • Aggressive = within 3 tricks
  • Super-Aggressive = within 4 tricks
My own personal scale might be closer to the rule of 2, 4 and 5! The scale you use doesn't matter as much as correctly recognizing when to apply the brakes and when to accelerate. The rule of 2 and 3 suggests that Vul on Vul in second chair is just as good as NV on NV in 3rd chair, when, in fact, the former is 2 tricks of leeway and the latter is 4-5 tricks!
 
 
Examples
  
South
KJ10xx
x
xxx
Q10xx
W
N
E
S
P
P
?
Open 2. You are NV and pard is a passed hand. Gentlemen, the green flag is waving. Go! Go!
 
South
KQJ10xx
x
xxx
xxx
W
N
E
S
?
Open 3. You are NV and your hand is pure. Yes, partner is unpassed but at least being NV will limit the damage from any game you miss. 3 will be far more damaging to the opponent's constructive auctions than 2.
 
South
xx
x
Q10xxxxx
Kxx
W
N
E
S
?
Pass. Vul on vul facing an unpassed hand is not the time for stepping out. If you open 3 and partner bids 3NT, he will be disappointed. Your preempt ought to show something like: AKxxxxx, AQTxxxx, KQT9xxx. Holding one filling honor, partner should be able to count on running the suit in 3NT. 
 
South
KJ109xxx
x
Qx
xxx
W
N
E
S
P
P
?
Open 3. Vul on vul is normally a yellow flag for preemption, but because partner is a passed hand there is little danger of missing a game, so our aggression is restored.
 
 
Conclusion
Vulnerability changes both the costs and the rewards of preempting. In general, our vulnerability is far more important than theirs. When we are vulnerable, it increases our potential costs all the time. When they are vulnerable, it only improves our rewards if they can also make a game. So aggressive preemption NV, and cautious preemption Vul is a good simple guideline. However, we can tune that further. 
 
When you are vulnerable, you can relax the cautious approach when partner is a passed hand. Missing a vulnerable game is not a concern, so loosen up. When you are NV, you can preempt aggressively in general. If you are NV and partner is a passed hand, go wild. 
 
Both the old rule of 2 and 3 and the more recent rule of 2, 3 and 4 for more modern players, are unreliable guides to preemption because they focus on how high to preempt, rather than when to preempt. If you want to preempt like a pro, base your preemption style on seat position and your vulnerability instead.
 
  
Parting Tips
  • Undisciplined preempts are vastly safer when partner is a passed hand.
     
  • Vulnerable preempts in a minor suit facing an unpassed hand should suggest that the suit will run facing one top honor. (AQxxxxx, KQxxxxx, AKxxxxx, etc.) 
     
  • When NV, err in favor of aggression; when Vul, err in favor of caution.
     
  • Fear the missed game, not the telephone number. 

  • Preempt when there is a lot to gain and little to lose. Pass when there is a lot to lose or little to gain. NV facing a passed hand has a lot to gain and little to lose. Vul facing an unpassed hand has a lot to lose. If you are preempting at a similar frequency and on similar hands in both scenarios, something is wrong.
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