These studies compared children living close to nuclear plants – within 5 km (3 miles) – to children living further away. Several epidemiologic studies in Europe have found excess childhood leukemia among children living near nuclear power plants. It’s easier to detect the effect of larger exposures, for example of nuclear workers, than the effects of smaller exposures, for example of people living near nuclear facilities. Furthermore, radiation exposures of most nuclear workers are monitored, whereas exposures of residents are not. This presents a big challenge, because an epidemiologic study that cannot sort people correctly into exposed and unexposed groups cannot detect an effect of exposure. There are many perils of epidemiologic studies, especially ones focused on low-level exposures. However, if epidemiologic studies are not well-designed, they can be used to dismiss the public’s concerns and avoid implementation of public health protections. People living near nuclear facilities may see an epidemiologic study as a way to shed light on their health concerns. The National Academy of Sciences is currently working on a request from the Nuclear Regulatory Commission to design an epidemiologic study of cancer around nuclear facilities in the USA. Members of the public and scientists have been concerned about environmental contamination from nuclear weapons and nuclear power generation for a long time.