Draw possibility criterion?

[friends]

Sometimes (for example when deciding playing turn or not with medium/bottom pair) it recommends to do this if you have the chance of having draw or straight nuts on the turn: you have 3 of 5 needed cards.
The possibility of getting, for example, two more spades on the turn and river (if you already have 3) is about 4%, and pot odds shold be at least 1:25 and even more, (cause probably you will have to pay a bet on the turn for you draw).
So, the question:
Is it really worth regarding such criterion?

[olavfo]

A backdoor draw to the nut straigh or nut flush can be worth as much as 1.5 outs. This can be enough to change a fold to a draw.

For example, you have flopped bottom pair, an ace overcard and a backdoor nut flush draw. Let's say the pot is offering you 6 : 1 and there's one bet to you. If you only had the bottom pair and an ace, you would have 5 outs to 2 pair or trips (which we'll assume is good enough to win), and you must fold, since you need pot odds 8.4 : 1, to call and see the turn card.

With the nut flush draw, you have 6.5 outs and now you only need 6.2 : 1 to call. Since the pot is offering you 6 : 1, you can call. (Strictly speaking, you need 6.2 : 1, but you'll probably make a bet or two on later rounds if your draw come in, so 6 : 1 is ok for a call.)

So you see that a backdoor draw changes the math significantly.

olavfo

[Shillx]

Let's assume that you have one opponent that has a hand that you can only beat by backdooring a flush. It will come in 4% of the time to make things easy. Only one bet goes in on each street. How big does the pot need to be in order to call?

EV = 0 = - 24*1 SB - 4*2 SB + (5+X SB)
X = 27 SB

Now let's say that there are 4 people in the pot instead of just one. Also assume that they will each give you 2 bets on the river when you hit. Now how big does the pot have to be?

EV = 0 = - 24 SB - 8 SB + (28+X)SB
X = 4 SB

So it really depends on a lot of different factors...

1) Are those your only outs
2) How many people are in the pot
3) How many bets will you have to pay on each street
4) What your implied odds are

In general, you should not chase backdoor draws unless you have some other kind of draw to go with it (like bottom pair or a gutshot). If the pot is big + multiway, you can peel with just a BD draw if you are pretty sure that you only have to pay one bet on the flop. If you have to pay a double bet on the flop, you are screwed...

Again, 4 people and you get a double on the river from everyone. This time though, you will have to pay 2 bets on the flop...how big must the pot be to call?

EV = 0 = - 48 SB - 8 SB + (32+X)SB
X = 24 SB

Brad