Statistics and Probability · Random variables

Expectation and variance

The long-run average value of a random variable, and how spread out it typically is around that average.

Also known as: expected value, mean of a random variable, variance of a random variable.

Start a lesson on Expectation and variance

Learn first

• Discrete random variables: A number assigned to each outcome of a random experiment, when only countably many values are possible.

Leads to

• Joint distributions: How two random variables behave together, including whether knowing one tells you anything about the other.
• Law of large numbers: A sample average gets closer to the true average as you collect more data.

Related topics

• Joint distributions: How two random variables behave together, including whether knowing one tells you anything about the other.