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.。
