The evolution of medical research has vaulted randomized clinical trials to the status of current gold standard of clinical evidence. In parallel, the evolution of the science of decision-making has revealed human beings' universal tendency to make biased judgments and systematic errors in their evaluation of information and choices. As a result of numerous psychological biases, randomized clinical trials are more prone to error, misinterpretation, and faulty judgment than is often acknowledged. Interdisciplinary fields of experimental psychology, economics, and social science are drawn upon to examine psychological biases in the interpretation of clinical evidence. A number of these are postulated to be important, both for the investigators generating clinical evidence and for the clinical observers interpreting clinical trials. This study focuses on the field of psychiatry and on the potentially significant implications of evidence biases for psychiatric practice and clinical understanding.