在坎福德郡爆发了脑膜炎球菌病，脑膜炎球菌感染的来源是无症状携带者，因此使用咽拭子培养进行了人口调查。在一个月的时间里，从500人的棉签中发现了69名病毒携带者。An outbreak of meningococcal diseaseoccurred in Camfordshire. Because symptom-free carriers are a source ofmeningococcal infection, a population survey was carried out using throat swabcultures. During one month 69 carriers of outbreak strains were identified out of swabs from 500 people.Which one of the following answers iscorrect?a) Theincidence of carriers was 13.8%b) Theincidence of carriers was 138 per thousand per monthc) Theprevalence of carriers was 0.138d) Neitherincidence nor prevalence may be calculated since the population of Camfordshireis not given
Answer
Incidence is the measure of new cases in a given time period and has units of cases per population at risk per time period. Prevalence is the measure of the number of cases at a single point in time and has no units. Incidence is measured in longitudinal studies of people initially disease free. Prevalence is measured in cross sectional surveys. Although this study took a month to carry out, the swabs only measured carrier status at one time point for each person and this is a cross sectional survey. The population of Camfordshire is irrelevant to calculating the sample prevalence. 中文解释：发病率是在指定时间段内分析新病例的量度，指的每个时间段处于风险中的每个人口的发生风险。患病率是对一个时间点的病例数的度量。 在对最初没有疾病的人进行的纵向研究中测量发病率，在横断面调查中测量患病率。 尽管这项研究花费了一个月的时间，但拭子仅在每个时间点测量了每个人的携带者状况，这是一项横断面调查。 坎福德郡的人口与流行率的计算无关。 所以答案是选择 C BMJ 统计问题系列新鲜上线！ 1.“BMJ统计问题”系列来了。每次一个小问题，配备中英文解释2.BMJ 统计问题（2）：t检验如何正确使用？3.BMJ 统计问题(3)：关于P值，哪种说法正确？4.BMJ 统计问题（4）：哪些因素会影响临床试验样本量计算？ 本号致力于医学科研方法分享，欢迎点击学习！
