对于正态分布 \(N(\mu, \sigma^2)\),数据落在不同标准差范围内的概率为:
\[ \begin{aligned} & P(\mu - \sigma \leq X \leq \mu + \sigma) \approx 0.6827 \\ & P(\mu - 2\sigma \leq X \leq \mu + 2\sigma) \approx 0.9545 \\ & P(\mu - 3\sigma \leq X \leq \mu + 3\sigma) \approx 0.9973 \end{aligned} \]