19. 随着上述研究的较长跟踪时期而带来的统计精确度提高，以及所观察到的癌症数量相应增多，都有助于考察剂量反应关系，特别是对低剂量来说。例如，关于日本原子弹爆炸幸存者的最新数据与各种剂量的线性或线性平方风险剂量趋势大体一致。但统计精确度方面的局限性、未被察觉的小偏差产生误导性结论的可能性以及在进行多次试验以确立可发现风险增加的最低剂量时完全偶然性地观察到具有统计意义的结果等等，都使仅限于低剂量的分析复杂化。对较大群体如原子弹爆炸生存者进行较长时间的跟踪，将会提供更多关于低剂量所产生的影响的信息。但是，仅凭流行病学是无法解决辐射风险是否存在剂量阈值这一问题的。必须对生物机制有更好的理解。特别是，使用流行病学方法无法查出剂量很低情况下的风险增加并不意味着癌症风险没有增加。
19. The increased statistical precision associated with the longer follow-up of the above studies and the resulting larger number of cancers observed has assisted in the examination of dose-response relationships, in particular for lower levels of dose. For example, the most recent data for the Japanese atomic bombing survivors are largely consistent with linear or linear-quadratic risk-dose trends over a wide range of dose levels. However, analyses restricted solely to low doses are complicated by the limitations of statistical precision, the potential for misleading findings arising from any small, undetected biases and the problem of observing statistically significant results purely by chance when performing multiple tests to establish a minimum dose at which elevated risks can be detected. Longer follow-up of large groups such as the atomic bombing survivors will provide more information on effects for low doses. However, epidemiology alone will not be able to resolve the issue of whether there are dose thresholds for radiation risks. A better understanding of biological mechanisms is necessary. In particular, the inability to detect increases in risks at very low doses using epidemiological methods does not mean that the cancer risks are not elevated.