外部效度（External Validity），是指实验结果类推到其他母体或环境的有效性（普遍适应性）。

外部效度是基于特殊科学实验的处理外部有效性，而对实验能否可以类推到其他母体或环境的推断。较高的外部效度可视为：

1. 可以类推到实验的目标群体
2. 可以类推到与实验类似的其他群体

External validity is the validity of generalized (causal) inferences in scientific research, usually based on experiments as experimental validity. In other words, it is the extent to which the results of a study can be generalized to other situations and to other people. Mathematical analysis of external validity concerns a determination of whether generalization across heterogeneous populations is feasible, and devising statistical and computational methods that produce valid generalizations.