Etiological Factors in Placebo Effect

Never before has there been so much interest in the placebo effect. Despite a greatly increased amount of research, the etiology of the placebo effect is not yet understood. This paper critically evaluates recently advanced concepts concerning the placebo effect, including personality of the patient, anxiety, catharsis, suggestibility, psychiatric diagnosis, constancy of effect, and the physician's interest. The physician's interest can be direct or indirect. The concept of indirect interest is advanced as an important subtle mechanism that may parsimoniously explain many observations about placebos.