Quantative estimates of human risk are now used for regulation and management of many technological, environmental, and occupational health risks. Ten or more years ago, this was not the case; except for activities for which reliable data were directly available (such as transportation risk) and for a few other areas (such as ionizing radiation), risk management decisions were made without quantitative risk estimates, although analytical methods that stopped well short of estimating risk were used.

Quantitative risk assessment is largely an invention born of the needs of risk policymakers. Risk assessment did not burst upon the regulatory scene as a result of a dramatic scientific advance, although the science behind risk assessment has improved in response to increased research funding. While it is tempting to associate the growth of quantitative health risk assessment with the remarkable advances in biology over the past decade, I do not think this is the case. The scientific approach to risk assessment for carcinogenic hazards is similar conceptually to methods that have been used to assess ionizing radiation since the early 1950s. The growth of quantitative methods for risk assessment in nonbiological fields—notably, in nuclear power plants—suggests that an anxious public and a politicized regulatory environment are the primary factors behind the recent growth in these approaches.