Internal Validity

In experimental psychopathology, one wants to ascertain that an outcome is the result of the experimental manipulation. For example, when a group of children display fewer symptoms of social anxiety after a series of group therapy sessions, one wants to know whether the symptom improvement in the children is really due to the therapy or due to some other factor that was not manipulated by the experimenter (e.g., the children simply got older during the experiment, which made their symptoms generally less severe). In other words, internal validity refers to the extent to which a causal conclusion (e.g., group therapy resulted in less severe social anxiety symptoms in children) based on a study is warranted. Thus, importantly, internal validity pertains to the following: (a) one ...