TheoremBase

Markov's and Chebyshev's Inequalities

The probability that a nonnegative random variable reaches a level a is at most its expectation divided by a, and the probability that a square-integrable random variable deviates from its mean by at least a is at most its variance divided by a².

Statement

In the setting of Probability Spaces: Notation, let a>0a>0 be a real number.

Markov's inequality. Let X∈M+(Ω,F)X\in\mathcal{M}^{+}(\Omega,\mathcal{F}). Then

a P(X≥a)≤EX.a\,P(X\ge a)\le\mathbb{E}X.

Chebyshev's inequality. Let X∈L2(P)X\in\mathcal{L}^{2}(P). Then

P(∣X−EX∣≥a)≤Var⁡Xa2.P\bigl(|X-\mathbb{E}X|\ge a\bigr)\le\frac{\operatorname{Var}X}{a^{2}}.

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