The expected value (or mean) of X, where X is a discrete random variable, is a weighted average of the possible values that X can take, each value being. Definition of expected value, from the Stat Trek dictionary of statistical terms and concepts. This statistics glossary includes definitions of all technical terms used. This article is about the term used in probability theory and statistics. For other uses, see Expected value (disambiguation). In probability theory, the expected value of a random variable, intuitively, is the long-run. They only informed a small circle of mutual scientific friends in Paris about it. Search Statistics How To Statistics for the rest of us! Find an Expected Value by Hand Find an Expected Value in Excel Find an Expected Value for a Discrete Random Variable What is an Expected Value used for in Real Life? Basically, all the formula is telling you to do is find the mean by adding the probabilities. Going back to texas holden rules first example used above for expectation involving the dice game, we would calculate the standard deviation for this discrete distribution by first calculating the variance:.