设随机变量 XXX 的数学期望和方差都存在,则对任意常数 ε>0\varepsilon>0ε>0,有
P(∣X−E(X)∣⩾ε)⩽Var(X)ε2P(|X-E(X)|\geqslant\varepsilon)\leqslant\frac{Var(X)}{\varepsilon^2}P(∣X−E(X)∣⩾ε)⩽ε2Var(X)
或
P(∣X−E(X)∣<ε)⩾1−Var(X)ε2P(|X-E(X)|<\varepsilon)\geqslant 1-\frac{Var(X)}{\varepsilon^2}P(∣X−E(X)∣<ε)⩾1−ε2Var(X)