Chebyshev Inequality

Theorem (Chebyshev Inequality)

For X∈L2X\in \mathscr{L}^{2}: P(∣X−μ∣≥α)≤Var(X)α2\mathbb{P}(|X-\mu|\ge \alpha)\le \frac{\text{Var}(X)}{\alpha^{2}}for all α≥0\alpha\ge 0.

\begin{proof} P(∣X−μ∣≥α)=P(∣X−μ∣2≥α2)≤E[∣X−μ∣2]α2\mathbb{P}(|X-\mu|\ge\alpha)=\mathbb{P}(|X-\mu|^{2}\ge\alpha^{2})\le \frac{\mathbb{E}[|X-\mu|^{2}]}{\alpha^{2}} with the inequality being an application of Markov’s Inequality. \end{proof}

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