Expected Value Expected value (EV) is a gaming concept you have to understand. You earn money long-term at the poker table by exploiting the errors of your opponents. The worse they play, the more money you can make. When you are losing long-term, you are the one who is making more errors than the opponents. An error in poker is when you play different than you would play as when you would know all cards of your opponents. In each hand you have to make decisions. And as you don't know the cards of your opponents and their reactions, you will make (theoretical) errors. Big mistakes occur when a player makes a decision that has a very high negative expected value, whereas a small mistake is when one gives up a small amount of expected value.
The concept of expected value now tries to optimize your bets. Optimal is to bet the maximum when you will win the hand and fold when you will lose the hand. This means you have to maximize your overall expectation. Expectation is the amount of money you will win or lose on average by making a bet. To calculate the expectation you take the average of all possible results and weight them by the likelihood of each one. Example: You are the button and you have   preflop in a $1/$2 NL game. A tight UTG player bets $15 and everyone is folding to you. (as he is tight you expect that he has a high pair - AA, KK, QQ, JJ, TT - or AK, AQ) His stack and your stack are $200 each. (Stack sizes are important for the decision)
Should you call or fold or raise? Math says that you will flop a set about one time in nine (8:1). Currently you have to bet $15 to win $18. But when you hit your set and he has a high pair you expect to win much more, often his whole stack. Maximum you can win is his stack size, as your both stacks are the same. The expectation for a call now is ( 8 * -$15 ) + ( 1 * $200 ) = -$120 + $200 = +$80 The expectation for folding is zero, which is less than +$80. So calling is (much) better than folding. A raise is also possible. Your opponent is tight, so he raised with a good hand and will not fold. For our calculation let's assume also, that he will not reraise (although he might do this with AA, KK or AKs) We raise to $30. The calculation now is: ( 8 * -$30 ) + ( 1 * $200 ) = -$240 + $200 = -$40
So our raise lowered our expectation. At the table you dont't have to calculate always your expectations like above. In the example above it is enough to know that your and your oppents stack should be higher than 8x his bet. In these cases you have positive expectation to call. What happens when the stack of the raiser is only $40 in the example above? Then the expectation is ( 8 * -$15 ) + ( 1 * $40 ) = -$120 + $40 = -$80 This is lower than the expectation for folding ( which is still 0 ), so you should fold. The problem is that his stack size is too small to give your call a positive expectation. Expected Value and Bluffing Bluffing and calling bluffs depend also on Expected value. When you make a bluff, you should estimate the bluff's chance of success. This chance of success should meet with a positive expectation. For example, if the pot is $100 and I make a bluff of $50, I need at least a 33% of the bluff's working (assuming I have 0% chance of winning if I am called). This is because I need to win 1 out of 3 times in order to break even.
Last update : 13-10-2007 16:27
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