the American Political Science Association held its first conference. In 2012, Bond et al.'s experiment delivered political mobilization messages to 61 million Facebook users. They aimed to explore whether an “I Voted” widget that announced one’s election participation to others increased turnout among Facebook users and their friends. Today's mature social media provide the opportunity to intervene experimentally with a vast capacity population. In 2014, the first issue of the Journal of Experimental Political Science was published by the Experimental Research section of the American Political Science Association. From 2010 to 2019, there were 75 articles using experimental methods published in American Political Science Review. The figure was 76 from 1950 to 2009 in this journal. Current experts in experimental methodology in political science include Rebecca Morton and Donald Green. Among the areas that it is used in are: Political psychology, including survey methodology, loss aversion, influences on voter turnout, and media influence; The effects on outcomes of different voting systems (e.g., storable votes), including the study of tactical voting; The political economy of development; International relations Interactions and voting in legislatures (and other deliberative assemblies), including the effects of different voting methods and control of the agenda. What makes a good experiment? Validity Social scientists, including political scientists, have long used validity to measure whether a particular analytical method can provide credible evidence for validating theoretical inferences. Donald Campbel defines validity as the validity of an empirical research design or method as the degree of approximation between the knowledge inference based on the design or method and the actual situation. Alternatively, validity is the extent to which we can believe that the empirical inference can reflect the real laws of human society. This definition has been recognized by most scholars. Validity can be further divided into internal validity and external validity. Campbell further refined the internal validity into three parts: constructive validity, causal validity, and statistical validity. Classification of validity aims to facilitate researchers to describe and conduct research from different aspects. Validity itself is a holistic concept. Any single class cannot exist in isolation from other validity. For example, high construct validity means that the research design has a higher degree of fit with the theory being studied. This makes the relationship of causal variables more stable from the statistical perspective, which supports the improvement of statistical validity. Internal validity is a prerequisite for external validity. If a