《英国医学会杂志》(BMJ)自2008年9月开始至2015年由两位流行病与统计学专家不间断地出了300多期statistical question系列。在这个系列中,两位学者每次出一道统计学选择题,进行选择并解释。现在我精选300道Statistical Question,形成中文版,请有兴趣的朋友们进行回答。 最近5期 BMJ 统计问题(6)发病率还是患病率? (7)这是何种流行病学研究设计类型?(8)关于疾病的“风险”,你懂得计算吗?(9)相对危险度(RR)的置信区间,哪一项可能是对的?(10)随机对照试验的“风险”,你会计算吗? BMJ 统计问题(11):相对危险度,你会计算吗?去年,一个县每月报告的平均自杀人数为3.2。为了比较月份之间的自杀次数,我们将计算P值或置信区间,为此,需要了解自杀人数的概率分布。 QuestionThe average number of suicides reportedeach month in one county last year was 3.2. To compare numbers of suicidesbetween months, calculating P values or confidence intervals, which probabilitydistribution would be most appropriate to use?A.BinomialB.NormalC.PoissonD.Weibull AnswerThe Poisson distribution describes the occurrence of rare events happening at random in a large population, which fits the bill here. It is also necessary to check that there are not linkages between the suicides, or clustering, as this will affect the interpretation of the expected probabilities. the Poisson distribution is helpful for ‘back of the envelope’ calculations because, when the number of events is reasonably large, the standard deviation of the distribution is the same number as the square root of the mean. (Technically the binomial distribution could be used but it requires long calculations of large numbers.) 中文解释:泊松分布描述了在大量人群中随机发生的罕见事件的发生,这很符合此处的情况。当然注意的是,需要检查自杀之间或聚类之间是否没有关联,因为这会影响对预期概率的解释(如果数据聚集性,泊松分布不成立)。泊松分布对于只需要粗略计算(back of the envelope calculations)的研究很有帮助,因为当事件数量相当大时,分布的标准偏差与均值的平方根相同。(从技术上讲,可以使用二项式分布,但需要对大数进行长时间的计算。) 所以答案是选择 C