Considered monitoring of the ratio of two correlated normal random variables based on an approximation. In this note, we derive a closed form expression for the ratio of two correlated normal random variables. We point out that the approximation used in Nguyen et al. does not always perform well.

中文翻译：

---

关于“使用可变采样间隔指数加权移动平均控制图监视两个正态变量的比率”的注释

考虑根据近似值监视两个相关的正常随机变量的比率。在本说明中，我们为两个相关的正常随机变量之比导出了一个封闭形式的表达式。我们指出Nguyen等人使用的近似值。并不总是表现良好。