ANIMAL MODELS OF PSYCHIATRIC ILLNESS Animal Models: Types Of Validity

important criterion for developing animal models to study psychopathology involves establishing the validity of the model as a true representation of the process being stud-ied. Generally, three types of validity are applied to animal models: face validity, construct validity, and predictive va-lidity (1–3). Face validity refers to the outward similarity in appearance between the model and the illness. Construct validity, on the other hand, does not exclusively involve outward tangible signs of the modeled illness. Rather, it refers to the internal mechanism or state that underlies the illness. Finally, predictive validity refers to the ability of the animal model to identify therapeutic treatments for the illness. It should be noted that the different types of validity can be independent of each other; an animal model can possess predictive and construct validity without possessing face validity. Ideally, an animal model should possess both construct and predictive validity so that it may be used to understand the mechanisms and etiology of the disorder and also to identify promising treatments for the disorder. Endophenotype Approach Species differences in the manifestation of a particular inter-nal state can cloud the usefulness of face validity in animal models. In addition, when considering a complex psychiat-ric illness, it is likely that several different symptom clusters contribute to the final pathologic condition; these different sets of symptoms may have different underlying substrates and thus may be ameliorated by different treatments. There