See also
At the time of the flop, you have two useful bits of information. First, you know how much other players who are still participating in the hand have bet before the flop. Second, you can approximate the majority of players' pre-flop starting hand criteria fairly accurately.
Pre-flop betting patterns used during a unique hand - particularly, the timing of calls, raises, re-raises, and check-raises - communicate players' opinions about the relative strength of pocket card holdings. If you think carefully about a hand of Texas Hold'em, betting is the only action a player absolutely needs to perform in order to talk with other players. Within the limits of the game, betting says everything. Other sorts of communication at the table are unnecessary.
Using betting patterns to read a player's hand must be done with awareness of the pitfalls. Since betting patterns are the primary means of communicating, they are also the primary means of creating deception. Hence, the predictive value of pre-flop betting patterns varies greatly from player-to-player and hand-to-hand. For example, we have noticed a trend toward slow-playing AA and KK in tournament play (that is, simply calling these premium hands before the flop to set a trap). Therefore, a player who suddenly turns into a calling station, after previously exhibiting normal calling and raising patterns, should be suspected immediately.
The most important information you get from the fact that another player is willing to see the flop is based on the fact that the great majority of players use similar distributions of starting hands in deciding to enter pots. If you were to survey the literature of Texas Hold'em, you would find little difference among authors regarding the general distribution of recommended starting hands.
We all learn almost identical starting-hand distributions when we start playing Hold'em. While players tend to expand starting-hand distributions as they gain experience, very few players are willing to play a large number of hands starting with any two random cards. (Why? Because you will lose a lot of dough unless you are extremely skilled and clever at playing after the flop, or the people you are playing against are totally unaware. Neither of these conditions are common in real life.) Almost any sensible set of criteria used to narrow starting hands down from any two cards results in a distribution of hands falling into a range of 25 to 35 percent of total starting hands.
More importantly, the expected value of a given hand that you may hold varies little whether your opponents distribution is fairly tight or fairly loose. As a result, you do not need to spend a lot of effort trying to "put your opponent on a hand" - you already know what he probably has. And, it matters very little if you are slightly wrong (we understand that in high stakes limit games, this "very little" can actually be the source of your edge. If you are going to play high stakes limit games, get your black belt in Hold'em first), so long as your opponent is using a reasonable range of possible distributions.
Here is an example of what we are talking about. Assume you are heads-up on the flop with another player, and you are holding KQ (hearts) in the pocket. Against a player who plays a starting hand distribution that includes 30 percent of possible pocket hands, you will win 55 percent of the time if you are holding a KQ (hearts or any other suit). Against a player who plays 20 percent of possible starting hands you will win 51 percent of the time. The decision-making value of the KQ (hearts) for you versus these two distributions is virtually equal, even though a 30-percent distribution contains 400 possible hands and a 20-percent distribution contains only 270 hands. Your KQ (hearts) will win 51 to 55 percent of the time. There is not enough difference in how well you do against either set of starting hands, at reasonable limits, for you to be overly concerned about which one is actually being used.
We feel highly confident making the assumption that a significant majority of players will play starting-hand distributions which are limited to a range of about 25 to 35 percent of possible starting hands.
The conclusion here is this: If a player is in the hand with you at all, he has a very high likelihood of holding cards from a distribution of hands that is well known to you and that has fairly low sensitivity with respect to the expected value of your hand against those distributions. Further, the wider the distribution of your opponents' starting hands, the larger the expected value of your own hand and the greater your overall advantage from playing a sensibly limited range of starting hands.
