The need to estimate risks

In an increasing number of situations, it is becoming possible to obtain and compare numerical estimates of the biological risks involved in different alternative sources of action. In some cases these risks are similar in kind, as for example when the risk of inducing fatal cancer of the breast or stomach by X-ray screening of a population at risk, is compared with the risk of such cancers proving fatal if not detected by a screening programme. In other cases in which it is important to attempt a comparison, the risks are dissimilar in type, as when the safety of occupations involving exposure to radiation or chemical carcinogens is compared with that of occupations in which the major risks are from lung disease or from accidental injury and death. Similar problems of assessing the relative severity of unlike effects occur in any attempt to compare the total biological harm associated with a given output of electricity derived from different primary fuel sources, with its contributions both of occupational and of public harm.