Why not double soft 19 against dealer 3-5

If you had a 9 you would double against 3-6. It seems there is a better chance of improving your hand if you double on a soft 19 vs a 9. You have all the good cards doubling on a 9 offers (9,10,A) plus the 2 for a chance to make 21. The basic strategy cards only show doubling on soft 19 against a 6. Does anyone know why this is? Is there something obvious that I am missing. I am just trying to consider this logically.

Quote: Username

...It seems there is a better chance of improving your hand if you double on a soft 19 vs a 9. You have all the good cards doubling on a 9 offers (9,10,A) plus the 2 for a chance to make 21...I am just trying to consider this logically.

Yes, the expected value (EV) of a doubled soft 19 is better than the EV of a doubled 9 because 19 + 2 = 21 whereas 9 + 2 = 11. However, don't compare soft 19 vs 9. The correct comparison to make is the EV of doubling soft 19 vs the EV of standing on 19. Here are some approximate EV's against various dealer up cards in a H17 (dealer hits soft 17) game:

Dealer	Double soft 19	Stand on soft 19
2	0.24	0.38
3	0.29	0.40
4	0.35	0.42
5	0.40	0.44
6	0.46	0.45

Look at the row for the dealer's having a 3. The EV of doubling a soft 19 is 0.29, but the EV of standing on 19 is 0.40. So, you will make an average of 0.40-0.29=0.11 more by standing on this hand than by doubling it.

Now, look at dealer's 6. What's your correct decision there?

Quote: ChesterDog

Now, look at dealer's 6. What's your correct decision there?

Be a chicken and stay. :)

Quote: Username

If you had a 9 you would double against 3-6. .

16 or less wins only if dealer busts, 17 sucks and loses most of the time, 18 is barely better; but 19 by itself is strong. If you take another card you clearly weaken your soft 19 hand a proportion of the time. With 9 you want more cards anyway, so the comparison is not good.

Quote: Username

If you had a 9 you would double against 3-6. It seems there is a better chance of improving your hand if you double on a soft 19 vs a 9. You have all the good cards doubling on a 9 offers (9,10,A) plus the 2 for a chance to make 21. The basic strategy cards only show doubling on soft 19 against a 6. Does anyone know why this is? Is there something obvious that I am missing. I am just trying to consider this logically.

YES, you are missing something. Never do something based on logic unless that's the best resource at hand! If the resource exists and you don't have it at hand.....................not advisable.

Would you stand with a 9 vs any dealer up card? No. Never.

But you WOULD stand with a 19. Ditto for a soft 19. It's a very strong hand. Leave it alone.

Quote: Username

If you had a 9 you would double against 3-6. It seems there is a better chance of improving your hand if you double on a soft 19 vs a 9. You have all the good cards doubling on a 9 offers (9,10,A) plus the 2 for a chance to make 21. The basic strategy cards only show doubling on soft 19 against a 6. Does anyone know why this is? Is there something obvious that I am missing. I am just trying to consider this logically.

The mathematics of choosing the best option is not rocket science, but it is tedious. The Wizard was kind enough to make his spreadsheet for infinite number of decks available on his website. I would suggest that you download it and try and follow the mathematics. It isn't that difficult. For infinite decks the best choice is to stand with a soft 19 against all dealer cards.

For a real game with less than infinite decks, there are some cases where you might double a soft 19.

The entire point of doing the calculation mathematically, is that no human being can see through all the possibilities for every case and add up which one has the advantage.

Go to Appendix 1 download the spreadsheet at the bottom of the page, and look at the formulas. He uses the results to develop the strategy boxes.