There is a distinction that one learns about on the first day of a course in psychological research methods. It is the difference between internal and external validity. Internal validity is ...

The information needed to determine the internal and external validity of an experimental study is discussed. Internal validity is the degree to which a study establishes the cause-and-effect ...

The following discussion is based on the framework of Campbell and Stanley, [1] in that specific threats to establishing a cause-and-effect relationship (i.e., internal validity) are associated with ...