In general, the concept of internal validity refers to the degree to which causal inferences are warranted on the basis of a study. Internal validity is thus largely a function of how well a study’s design and execution allows researchers to make definitive claims about the causal relationship between one or more independent variables and one or more dependent variables and rule out alternative (i.e., noncausal) explanations for observed associations. Internal validity is often contrasted with external validity, which refers to the extent to which the results of a study can be generalized to situations and people outside the scope of the study itself. It should also be noted that (unlike many uses of the term validity in educational and psychological research), the phrase internal ...