The brave new world of lives sacrificed and saved, deaths attributed and avoided.

Attributable risks are routinely estimated in "risk-factor" epidemiology. Often, these risks are interpreted as the numbers of deaths caused by (or numbers of lives lost by) exposure to the factor of interest. It is then often surmised that removal of exposure will avoid deaths and save lives. This reasoning leads to confusion because of 2 underlying assumptions. One is that removal of the exposure will reduce permanently the annual number of deaths by the number attributed to the factor. In reality, deaths are merely postponed and lives are merely prolonged; estimating the effect of exposure on life expectancy is both more straightforward and of greater public health interest. The other misleading premise is that the deaths attributed to a certain risk factor can be identified. While such identification may be possible for certain immediate external causes of death (eg, accidents), it is not usually feasible for deaths attributed to factors that merely contribute to development of chronic disease and ultimately death. For such exposures, it is more reasonable to suggest that they contribute to death in all who are exposed - more so in some people than in others. Again, it is more appropriate to calculate the average loss of life expectancy associated with exposure from follow-up studies; the years of life lost by individuals who are exposed then varies around this average. The "real age" concept popularized in lifestyle Web sites and television programs may be more useful than calculations of the numbers of attributable deaths for communicating individual as well as public health risks associated with common environmental, occupational and lifestyle risk factors.