EV (expected value) is one of the most importent aspects in all sorts of gambing. EV in poker can be measured in many ways - some ways less exact then others. One importent area in poker that will vary from positive to negative EV is the starting hands.
Poker EV graph

This diagram shows the best starting hands in Texas hold'em and their EV based on the amount of big blinds they win in the long run (the numbers is based on over 100 millions dealt pocket cards played at full tables in Poker Room). AK indicates off suited and AK suited.
+ EV and - EV

The last diagram shows us an example of + EV (positive expected value) and - EV (negative expected value). Also this time the focus lays on starting hands and here we have a collection of marginal hands (the numbers is based on the same information as mention above).
How to think about EV and use the given information
The EV tells us then to play and when to pass. It's simple but on the same time not. We have learn some about which starting hand that works well in a certain playing condition, but where is always more things to care about. EV in poker are complex just because Poker is a complex game. We are dealing with lots of inperfect information and how to succeed is to make a good judgement on many factors. This will come with knowledge and with plenty of knowledge you will make better approximations about the EV in the situations that turns up on the table.
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