| 简介： | Abstract: The common theme is that approaching the EV problem hinges on assumptions about the relationship between the population from which one has internally valid estimates and the population about which one tries to make judgments. Except these researches on EV in specific context, most researches either ignore the EV problem or take it subjectively. So in this paper we provide a formal and general reflection on the EV problem and propose a simple and generally applicable measure that evaluates external validity for RCTs. |