AI engineering glossary · Probability
What is variance?
Variance: A measure of how spread out a random variable is around its mean: Var(X) = E[(X - mean)^2] = E[X^2] - (E[X])^2. Larger variance means values are more scattered and less predictable. Its units are the square of the variable's own units.
Variance: an example
Two shops both average 100 sales a day; one always sells 95 to 105, the other swings from 20 to 180. The second has far greater variance.
Related terms
More Probability terms
- Z-score
- Addition rule
- At-least-one probability
- Base rate
- Base rate fallacy
- Bayes' theorem
- Bayesian probability
- Bernoulli distribution
Where you learn it
Variance is part of the AI Engineering Program, which teaches it with notes, a hands-on lab and an exam. The first lesson is free.