Summary
The ABCC program has been of great value both scientifically and humanistically, and it has been all the more impressive in the light of the difficult conditions under which it has had to operate. The new binational leadership should maintain and strengthen the program. Massive data meticulously collected for nearly two decades have demonstrated heretofore unknown relationships between radiation dose and later adverse human effects. Further studies should continue to yield important information, especially on the incidence of specific types of cancer, on the kinetics of radiation induced neoplasia, and on mutagenesis. This unique population should continue to be investigated for at least two more decades, by which time persons exposed during embryonic development or childhood will have passed middle age.

The wisdom and foresight of the Francis Committee are borne out by the obvious competence of the epidemiologic studies. By clearly defining the various samples, by carefully matching groups with different exposures, and by observing them longitudinally in a systematic manner, the ABCC studies have set a high standard of epidemiologic rigor.

The early demonstration of a large increase in the relative risk of leukemia in the exposed group and the association of the risk with the dose have been of great value, not only in increasing understanding of the disease, but in the setting of national and international radiation standards. Although the incidence of leukemia is subsiding, the incidence of other forms of malignancy is increasing; it is of the greatest importance that these studies continue, so that malignancies with very long latent periods may be identified.

The early genetic studies on the children of exposed parents showed that the genetic risk is not as large as some had feared; in fact, no significant differences in the children of irradiated and control populations were discovered. These observations emphasize another aspect of the program: a great many studies have failed to demonstrate a significant difference between irradiated and control populations. Many of these involved large numbers of people who were heavily irradiated, and they therefore have a high statistical precision. It is important to emphasize that negative results are as important as positive ones, especially in a context where an a priori basis for fear existed. Statements of nonsignificant differences accompanied by statements of the precision of the measurements enable one to put upper limits on radiation damage. Such conclusions are among the most important results of the study.

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