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Since the atomic bombings of Hiroshima and Nagasaki in 1945, and the subsequent reports of raised cancer risks among survivors in the two cities, there has been interest and concern about risks arising from this and other nuclear incidents, such as the 1986 Chernobyl accident. This article reviews methodological aspects associated with the detection of cancer risks in groups exposed to ionising radiation, summarises findings from relevant studies, and looks at possible future developments.
It should be emphasised that cancer risks have also been examined in a multitude of studies of radiation exposures from medical, occupational, and natural sources. Further details of these studies can be found in the most recent report by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR).1
METHODOLOGICAL ASPECTS
The ability to detect and quantify raised cancer risks in an epidemiological study depends on the study design. Particular aspects are as follows.
STATISTICAL POWER
Owing to random variation in data, it may not be possible to identify a raised risk in a small study. Therefore, before conducting a study, it is standard practice to calculate its statistical power. This is the probability that the study will detect a given level of raised risk with a specific degree of confidence—for example, the probability of detecting a doubling of risk using a significance test at the 5% level. For a cohort study, in which a cohort of individuals is followed to determine their subsequent disease incidence or mortality, the power depends on the size of the cohort, the length of time for which they are followed up, the baseline rate of cancer, the distribution of radiation exposures received by members of the cohort, and the putative radiation risk factor. For a case–control study, in which radiation exposures are compared for persons with the cancer of interest (cases) …
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Website extra Additional references appear on the Occupational and Environmental Medicine website www.occenvmed.com