principle of covariance

例句：

1. 1. In statistics, covariance is a measure of the relationship between two variables.
   在统计学中，协方差是两个变量之间关系的度量。
2. 2. The covariance of the variables is 0.5, indicating that they are perfectly correlated.
   这两个变量的协方差为0.5，表明它们之间完全相关。
3. 3. Covariance is often used in regression analysis to determine the impact of one variable on another.
   在回归分析中，协方差常被用于确定一个变量对另一个变量的影响。