Biomarkers in psychiatry: methodological issues.

Particularly in psychiatry, biological measures are increasingly sought to detect exposure to toxic agents, to assist in early identification of illness, and to enhance diagnostic certainty, provide prognostic information, and permit the mapping of outcome in a variety of disorders. The authors explore the fundamental criteria necessary to designate a biological measure as a "biomarker" and discuss the potential applications, limitations, and hazards of such markers. Authors discuss methods for establishing the validity of a biomarker. Finally, they convey a word of caution about overinterpreting the clinical or scientific value of any biological measure.