Suspicions about medical murder sometimes arise due to a surprising or unexpected series of events, such as an apparently unusual number of deaths among patients under the care of a particular nurse. But also a single disturbing event might trigger suspicion about a particular nurse, and this might then lead to investigation of events which happened when she was thought to be present. In either case, there is a statistical challenge of distinguishing event clusters that arise from criminal acts from those that arise coincidentally from other causes. We show that an apparently striking association between a nurse's presence and a high rate of deaths in a hospital ward can easily be completely spurious. In short: in a medium-care hospital ward where many patients are suffering terminal illnesses, and deaths are frequent, most deaths occur in the morning. Most nurses are on duty in the morning, too. There are less deaths in the afternoon, and even less at night; correspondingly, less nurses are on duty in the afternoon, even less during the night. Consequently, a full time nurse works the most hours when the most deaths occur. The death rate is higher when she is present than when she is absent.

翻译：对医疗谋杀的猜测有时是由于一系列意外或意外的事件而出现,例如护士护理下病人的死亡人数明显异常,但是一个令人不安的事件可能会引起对某个护士的怀疑,然后可能导致对她在场时发生的事件进行调查。在这两种情况中,都有一个统计上的挑战,即区分由犯罪行为引起的事件组群与与其他原因的巧合引起的事件组群。我们表明,护士在场和医院病房的高死亡率之间明显惊人的联系很容易是完全虚假的。简而言之,在中等护理病房,许多病人都患有绝症,死亡频繁,大多数死亡发生在上午。大多数护士在上午上班,下午死亡较少,晚上甚至更少;相应地,下午上班的护士更少,晚上甚至更少。因此,在大多数死亡发生时,全时护士工作的时间最多,因此,当她不在时死亡率要高于她不在时。