# Expected value

From Lesswrongwiki

Revision as of 04:20, 29 September 2009 by PeerInfinity (talk | contribs)

The **expected value** or **expectation** is the (weighted) average of all the possible outcomes of an event, weighed by their probability. For example, when you roll a die, the expected value is (1+2+3+4+5+6)/6 = 3.5.

(Since a die doesn't even have a face that says 3.5, this illustrates that very often, the "expected value" isn't a value you actually expect.)