Random assignment to parallel groups, the hallmark of an experimental study, effectively controls all threats to internal validity except experimental mortality. Differential selection is ...

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 ...