'The most interesting questions from visitors to the Dutch sister site (Bridgevaria.nl)'. 

Dear Ed & Peter,

What do I show when I double the opponents' 15-17 1NT opening?
I thought the message of the double is: 'I have a 1NT opening as well', but others tell me the double shows a normal opening. Which of the two explanations is the right one?

Regards,
Els

Reply Ed Hoogenkamp (South)

Dear Els,

Most experts agree that the doubler's point count should be at least equal to the upper limit of the 1NT opening. So doubling a 15-17 1NT opening requires at least 17 HCP and doubling a 12-14 1NT opening requires at least 14 HCP.
These requirements are based on risk calculation. Doubling a 15-17 1NT opening on a mere 13 HCP will sometimes turn out well (if partner has some points too) but relatively often it will not. In the latter case the doubler will shortly afterwards have to choose between defending 1NT redoubled (very expensive if they make it) and escaping (?) to a contract of his own, getting doubled and suffering a heavy penalty.
The risk of having to make such an awful choice is a lot smaller if the doubler has at least the same point count as the opener.

No doubt it's all different in Norway. They like to take risks over there, so I've been told. 

Un saludo, regards from Barcelona

Reply Peter van der Linden (North)

Dear Els,

Ed is right about the required point count. However he fails to explain the mathematics behind this risk calculation. The following line of reasoning often works at bridge. The idea is, that you stir into action (in this case: double for penalties) if the chance of your party having the majority of points is substantially better than 50% .
The 1NT opener has 15-17 HCP, on average about 15.7. If you have 17, you and opener have 32.7 between the two of you. That leaves on average (!) 3.65 for each of the other opponent and your partner. So you and partner have on average a combined 20.65 count, the opponents 19.35.
If you double on a mere 16 HCP, you and partner have a combined 20.15 count, making this double riskier.

(By the way: you haven't mentioned whether the double is in the direct position (the doubler is behind the 1NT opener) or in the balancing position (the doubler is before the 1NT opener, so he doubles after two passes). Ed hasn't bothered to distinguish between these positions (there was an important message, something about sangria and terrace, so he had to leave; he apologises). As a consequence of the mathematics above, the double in the balancing position requires fewer HCP since the partner of the 1NT opener has been proven to have less than 9 HCP, this changes the odds).

An example of a different kind of auction, in which you follow a similar line of reasoning:

If you have enough points and a suitable distribution (!) you may want to defend. You consider redoubling then: 'If possible I want to double them for penalties!'
How many points do you need to redouble? At least 9, for in that case you know you and partner have the majority of points (for those who open very lightly — nowadays some players open about any 11 count! — a lower limit of 10 is more appropriate). 

But the required point count is only part of the story. As is his habit, señor Hoogenkamp has taken the easy way out. After all, you state that in your view the doubler should have a 1NT opening himself. So you ask about the required distribution as well.
The answer is no. You can double with any distribution. Anything goes, provided that the double is likely to be profitable!
However, sound reasoning will always be a necessity, as this example from practice, starring Ed, shows:

Enthusiastically he put down the blue card (redouble) and dreamed of +1560 (nine tricks), +1960 (ten tricks) or +1100/+1400 (if EW chickened out).
East passed with a deep sigh, South passed with a neutral expression and West passed with a big grin. Too late Ed realised what was happening:

S/NS		♠	A J 2
		♥	Q J 6 4
		♦	5
		♣	K Q 5 4 2
♠	9 6 3			♠	8 7 4
♥	10 3			♥	9 7 5 2
♦	A K Q J 10 7 2			♦	8 6 4
♣	7			♣	10 9 6
		♠	K Q 10 5
		♥	A K 8
		♦	9 3
		♣	A J 8 3

¹ 15-17

Neither +1960 nor +1560 but -400 (down one)... As a final insult it turned out that NS could make 6♠ (+1430) and 6♣ (+1370).
Of course Ed should have realised that he and his partner had 28-30 HCP between them. So there was no way West could have 17 HCP. What on earth was West doubling on then? If Ed had taken a closer look at his hand and especially at the singleton diamond, the peseta probably would have dropped.
(What he should have bid instead of redoubling? Well, 2NT! That cannot be natural, since with a balanced 8-9 count North would redouble — or pass, if a redouble is artificial. So 2NT must be artificial and game forcing; NS now bid their suits up the line until a fit is found).

But seriously: this smart West player shows the importance of having a good suit to lead — after all, he is to lead himself — when considering doubling 1NT.
As a consequence not every 17 count qualifies for a double:

¹ 15-17

17 HCP but a double is ill-advised since it will tell South where the points are. The play will develop into a ping-pong match between West and South: every time West gains the lead, he will have to cede a trick.
The best West can do is to pass quietly, hoping for South to go down (after West's pass South is more likely to misplay the hand than after West's double, since after having seen some points in West, he will assume East to have the majority of the remaining face cards).

Only 15 HCP but this hand certainly is worth a double.

To sum it up:
- A double of their 1NT opening is for penalties: the doubler thinks there is a good chance of defeating the contract and obtaining a good score. If he has a (rather) balanced hand this means he should have at least the point count of the upper limit of the 1NT opening bid.
- If the doubler has a minimum, a good suit to lead is essential.
- If he has an extremely good and long suit, he can double on fewer points.

PS: On closer inspection I think that Ed was West in the example that ended in −400. After all, he is quite clever. He led the ♦J, commenting that it was fourth best, adding 'it's my middle diamond as well...'

En hils, regards from Orkanger