This method is easy to implement, but it only accommodates discrete covariates .

该方法的缺点是：考虑的协变量只能是分类变量。

Propensity scores are used to reduce selection bias by equating groups based on these covariates.

倾向得分通过平衡各组的协变量的方法,用于降低选择偏倚.

These covariates included family characteristics and previous problems with thinking, learning and memory.

这些影响因素包括家庭情况和先前思维、学习记忆能力问题。

These associations remained significant after adjustment for multiple baseline covariates but were not observed in the placebo group.

在进行了多因素调整后，以上两组中这种相关性仍然显著存在，但在安慰剂组则没有观察到有相关。

A third virtue, is that time varying covariates can be easily added to the model to determine how changes in these them influence the dependent variable.

第三，时间与共变不同，时间能够轻易地加入模型，并决定出在这些影响下可靠变量的变化。

These findings indicate that experienced PA, even over a single day, has a graded relationship with survival that is not caused by baseline health status or other covariates.

但研究人员也指出，这里所能证明的只是一种相关性，对于其中的因果关系还有待深入分析。