Some commentators have argued that physicians have duties to serve as role models for the general public in matters of health, for example by not smoking cigarettes.[33] Indeed, in most western nations relatively few physicians smoke, and their professional knowledge does appear to have a beneficial effect on their health and lifestyle. According to a study of male physicians,[34] life expectancy is slightly higher for physicians (73 years for white and 69 years for black) than lawyers or many other highly educated professionals. Causes of death which are less likely to occur in physicians than the general population include respiratory disease (including pneumonia, pneumoconioses, COPD, but excluding emphysema and other chronic airway obstruction), alcohol-related deaths, rectosigmoid and anal cancers, and bacterial diseases.[34]