Division of Law and Psychiatry, Yale University Department of Psychiatry, 34 Park Street, New Haven CT 06519, USA. alec.buchanan@yale.edu
Deciding whether someone is legally competent to make decisions regarding their own treatment requires an assessment of their mental capacity. The assessed capacity required for legal competence increases with the seriousness of what is at stake. The usual explanation is that patient autonomy is being balanced against best interests. An alternative explanation, that we require greater room for error when the consequences are serious, implies a change to clinical practice and in the evidence doctors offer in court.