- Overconfidence in clinicians was examined in two independently designed studies, each using a different research approach. The first study examined treatment choices of physicians in treating breast cancer, and the second rapid decision making among nurses working in Intensive Care Units. In both studies, individual respondents were highly confident they had made the right choice ('micro-certainty'), although there was no consensus across respondents as to what the optimal treatment would be ('macro-uncertainty'). The difference between micro-certainty of individuals and macro-uncertainty within the clinical community may cast some light on the persistence of practice variation. The implications of overconfidence in clinical treatment for patients, practitioners, and professional regulation are discussed.