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.
