4队列研究(群组研究)

介绍队列研究（cohort study）临床研究中，cohort study翻译成中文叫做队列研究，cohort这个词的原意是军队里的步兵，表示的是用一个群体中具有相似属性的人。

队列研究的证据强度在RCT（随机对照试验）之下，其最大特点是观察性和前瞻性，即研究者不对观察对象进行任何干预，而只是设立纳排标准，将符合的样本纳入进行观察，在不同的时点进行结局测量并进行数据分析。

队列研究也是分组的，只不过不像RCT，分为治疗组和对照组，而是分为了暴露组和非暴露组，其主要作用之一就是研究疾病与危险因素的关系。

以吸烟与肺癌的关系为例。

我们可以观察一群吸烟的人（此时为健康人）那么吸烟在这个研究中就属于暴露因素，我们可以同时期观察不吸烟的健康人群作为对照，那么这个对照用的群组就属于非暴露组，经过一段时间（此类观察性研究往往时间很长），可以是一年，十年，二十年，通过长期的跟踪随访，测量两组人群肺癌的患病率，那么肺癌在这里就是我们所要测量的结局。

另外在一些涉及伦理学问题或者患者依从性问题的临床研究中，队列研究有时候可以代替随机对照试验，比如在中医药的研究中，有时候把老中医开方子和安慰剂作对照进行RCT 患者不容易接受，我们就可以采用队列研究的方法，不干预，只观察，还有关于中医辨证论治的研究，cohort study也不失为一个很值得考虑的办法。

这方面曾经发过一个帖子，大家参考，欢迎讨论！/thread-94843-1-6.htmlcohort study的适用范围1，研究不大常见的治疗或者预防作用，就是之前讲的比如涉及到伦理学的问题2，探索疾病的病因，研究干预或者与干预相关的不良作用3，评价医疗服务提供方式和管理模式的效果4，探索疾病的预后cohort study的优点：1，研究可以事前计划2，可以计算发生率3，结果相对可靠4，相对容易完成缺点：1，研究的周期长2，难以收集大量样本，尤其是罕见的疾病3，因为耗时场，人员变动有可能很大，随访过程中，容易有病例流失4，这种研究方法理论上说不适用于评估干预措施的疗效5，研究结果难以重复结果相对可靠，是针对其前瞻性和长时间跟踪随访来说的，在随访当中，几乎没有病例能够逃脱检测，能够提供无偏差的药物暴露资料，且对暴露情况的评估不会由于疾病的流行性造成偏倚；由于是前瞻性的，不会像CCS一样出现回忆偏倚，在选择病例时，发生选择偏差的风险小于病例对照研究。

队列研究（cohort study 或panel study），又译为群组研究、定群研究、追踪研究、梯次研究等，是在医学、社会科学、精算学、生态学等领域中使用的一种纵向研究（longitudinal study）。

它是对风险因子的分析手段，通过对未患某一特定疾病的人群在一定时间内的观察，根据相关性来确定被观察对象患病的风险。

它是一种临床研究设计，应与横向研究（cross-sectional study）相互参照。

队列研究的对象大多是有特定生活经历的人群及其中的个人。

队列（cohort或panel）是指一群在特定时期内有共同特征或经历的人，如在某一时期出生或在暴露于某因素（如一种药物、疫苗、污染物或经历特定的医疗过程等）的人。

那些出生于某一天或某一特定时期的人被称为出生队列（birth cohort）。

与其作比较的对照组可以是普通人群，也可以是没有暴露（或少量暴露）于所研究因素的人群。

此外，队列中还可划分为小群以互相比较。

队列研究可以是前瞻性或回顾性的。

A cohort study is a form of longitudinal study（纵向研究） (a type of observational study) used in medicine, social science, actuarial science（精算学）, business analytics（商业分析）, and ecology（生态学）. For instance in medicine, it is an analysis of risk factors and follows a group of people who do not have the disease, and uses correlations（统计）to determine the absolute risk of subject contraction. It is one type of clinical（临床）study design and should be compared with a cross-sectional study（横向研究）Cohort studies are largely about the life histories of segments（片段）of populations, and the individual people who constitute these segments.A cohort is a group of people who share a common characteristic or experience within a defined period (e.g., are born, are exposed to a drug or vaccine or pollutant, or undergo a certain medical procedure). Thus a group of people who were born on a day or in a particular period, say 1948, form a birth cohort. The comparison group may be the general population from which the cohort is drawn, or it may be another cohort of persons thought to have had little or no exposure to the substance under investigation, but otherwise similar. Alternatively, subgroups within the cohort may be compared with each other.Randomized controlled trials (RCTs) are a superior methodology in the hierarchy of evidence in therapy, because they limit the potential for any biases by randomly assigning one patient pool to an intervention and another patient pool to non-intervention (or placebo). This minimizes the chance that the incidence of confounding (particularly unknown confounding) variables will differ between the two groups. However, it is important to note that RCTs may not be suitable in all cases and other methodologies could be much more suitable to investigate the study's objective(s).Cohort studies can either be conducted prospectively, or retrospectively from archived records.Cohort (statistics统计学)In statistics and demography, a cohort is a group of subjects who have shared a particular event together during a particular time span(e.g., people born in Europe between 1918 and 1939; survivors of an aircrash; truck drivers who smoked between age 30 and 40). Cohorts may be tracked over extended periods in a cohort study. The cohort can be modified by censoring, i.e. excluding certain individuals from statistical calculations relating to time periods (e.g. after death) when their data would contaminate the conclusions.The term cohort can also be used where membership of a group is defined by some factor other than a time-based one: for example, where a study covers workers in many buildings, a cohort might consist of the people who work in a given building.Demography often contrasts cohort perspectives and period perspectives. For instance, the total cohort fertility rate is an index of the average completed family size for cohorts of women, but since it can only be known for women who have finished child-bearing, it cannot be measured for currently fertile women. It can be calculated as the sum of the cohort's age-specific fertility rates that obtain as it ages through time. In contrast, the total period fertility rate uses current age-specific fertility rates to calculate the completed family size for a notional woman were she to experience these fertility rates through her life.In medicine, a cohort study is often undertaken to obtain evidence to try to refute the existence of a suspected association between cause and effect; failure to refute a hypothesis often strengthens confidence in it. Crucially, the cohort is identified before the appearance of the disease under investigation. The study groups follow a group of people who do not have the disease for a period of time and see who develops the disease (new incidence). The cohort cannot therefore be defined as a group of people who already have the disease. Prospective (longitudinal) cohort studies between exposure and disease strongly aid in studying causal associations, though distinguishing true causality usually requires further corroboration from further experimental trials.The advantage of prospective cohort study data is that it can help determine risk factors for contracting a new disease because it is a longitudinal observation of the individual through time, and the collection of data at regular intervals, so recall error is reduced. However, cohort studies are expensive to conduct, are sensitive to attrition and take a long follow-up time to generate useful data. Nevertheless, the results that are obtained from long-term cohort studies are of substantially superior quality to those obtained from retrospective/cross-sectional studies. Prospective cohort studies are considered to yield the most reliable results in observational epidemiology. They enable a wide range of exposure-disease associations to be studied.Some cohort studies track groups of children from their birth, and record a wide range of information (exposures) about them. The value of a cohort study depends on the researchers' capacity to stay in touch with all members of the cohort. Some studies have continued for decades.In a cohort study, the population under investigation consists of individuals who are at risk of developing a specific disease or health outcome.[4]An example of an epidemiological（流行病学的）question that can be answered using a cohort study is: does exposure to X (say, smoking) associate with outcome Y (say, lung cancer)? Such a study would recruit a group of smokers and a group of non-smokers (the unexposed group) and follow them for a set period of time and note differences in the incidence of lung cancer between the groups at the end of this time. The groupsare matched in terms of many other variables such as economic status and other health status so that the variable being assessed, the independent variable (in this case, smoking) can be isolated as the cause of the dependent variable (in this case, lung cancer). In this example, a statistically significant increase in the incidence of lung cancer in the smoking group as compared to the non-smoking group is evidence in favor of the hypothesis. However, rare outcomes, such as lung cancer, are generally not studied with the use of a cohort study, but are rather studied with the use of a case-controlstudy.Shorter term studies are commonly used in medical research as a form of clinical trial, or means to test a particular hypothesis of clinical importance. Such studies typically follow two groups of patients for a period of time and compare an endpoint or outcome measure between the two groups.Randomized controlled trials, or RCTs are a superior methodology in the hierarchy of evidence, because they limit the potential for bias by randomly assigning one patient pool to an intervention and another patient pool to non-intervention (or placebo). This minimizes the chance that the incidence of confounding variables will differ between the two groups.Nevertheless, it is sometimes not practical or ethical to perform RCTs to answer a clinical question. To take our example, if we already had reasonable evidence that smoking causes lung cancer then persuading a pool of non-smokers to take up smoking in order to test this hypothesis would generally be considered quite unethical.Two examples of cohort studies that have been going on for more than 50 years arethe Framingham Heart Study and the National Child Development Study (NCDS), the most widely-researched of the British birth cohort studies. Key findings of NCDS and a detailed profile of the study appear in the International Journal of Epidemiology.The largest cohort study in women is the Nurses' Health Study. Started in 1976, it is tracking over 120,000 nurses and has been analyzed for many different conditions and outcomes.The largest cohort study in Africa is the Birth to Twenty Study, which began in 1990 and tracks a cohort of over 3,000 children born in the weeks following Nelson Mandela's release from prison.Other famous examples are the Grant Study tracking a number of Harvard graduates from ca. 1950.77, the Whitehall Study tracking 10,308 British civil servants, and theCaerphilly Heart Disease Study, which since 1979 has studied a representative sample of 2,512 men, drawn from the Welsh town of Caerphilly.。

第五章：练习题库-流行病学和医学统计学1.（单选）正确答案：B。

考查疾病筛检试验的定义，记忆型题目；筛检(Screening)是指通过快速的试验、检查、或其他方法，在表面健康人群中将那些可能有病但表面健康的人识别出来。

2.（单选）正确答案：D。

考查流行病学研究方法的分类，理解记忆型；A为观察性研究；B和E为实验性研究；C为临床的诊断方法。

数学模型是流行病学方法研究的一种，为理论性研究。

3.（单选）正确答案：A。

考查统计描述的描述指标，记忆理解型题目；标准差和变异系数是描述计量资料离散趋势的指标；中位数通常是描述不对称资料（偏态资料）的集中趋势指标；几何均数是描述偏态分布资料另外一个重要指标；所以算术均数（通常简称均数）是描述计量资料的集中趋势指标，故选择A。

4.（单选）正确答案：B。

考查描述集中趋势的指标，理解型题目；标准差和变异系数是描述计量资料离散趋势的指标；中位数和几何均数通常是描述不对称资料（偏态资料）的集中趋势指标；算术均数（通常简称均数）是描述计量资料的集中趋势指标，本题身高按照实际情况，符合正态分布，其平均水平应选用算术均数，故选择B。

5.（单选）正确答案：C。

考查流行病学的定义，记忆型题目；流行病学不仅仅研究各种疾病，而且研究健康状态和事件，所以流行病学不仅仅只是研究传染病。

6.（单选）正确答案：C。

考查流行病学的定义，记忆型题目。

流行病学是研究人群中疾病与健康状况的分布及其影响因素，并研究如何防治疾病及促进健康的策略与措施的科学。

7.（单选）正确答案：A。

考查流行病学的概念，记忆型题目。

流行病学的研究对象是人群，所关注的是具有某种特征的人群，并不是从个体上研究疾病。

8.（单选）正确答案：D。

考查率的概念，记忆型题目；率是表示在一定的条件下某现象实际发生的例数与可能发生该现象的总例数之比，来说明单位时间内某现象发生的频率或强度。

9.（单选）正确答案：A。

考查发病指标与患病指标的内涵，理解型题目；若用普查的方法，则只能了解高血压在某个时间点或时间段的患病人数，而新发病例、该时间死亡人数等数值均无法得到，故只能计算患病率。