Abstract Making sound safety decisions requires accurate estimates of the costs of injuries and the benefits of their reduction. These estimates may be produced intuitively by citizens exposed to risk of injury, or formally, for analysts considering alternative safety policies. All such estimates rely on behavioral assumptions, regarding how people perceive and respond to risks. They also rely on ethical assumptions, regarding how people should respond. The nature and validity of these assumptions are analyzed here, in order to provide a consumer's guide to techniques designed to evaluate risks and devise safety policies.