Cohort-based Study

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A Cohort-based Study is an longitudinal study that assigns study members to cohorts (based on some predetermined rules).



  • (Wikipedia, 2015) ⇒ Retrieved:2015-1-10.
    • A cohort study is a form of longitudinal study (a type of observational study) used in medicine, social science, actuarial science, business analytics, and ecology. 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 to determine the absolute risk of subject contraction. It is one type of clinical study design and should be compared with a cross-sectional study. Cohort studies are largely about the life histories of segments 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.


Analytic study of epidemiological study in which subsets of a defined population can be identified who are, have been, or in the future may be exposed or not exposed, or exposed in different degrees, to a factor or factors hypothesized to influence the probability of occurrence of a given disease or other outcome. The main feature of the method is observation of a large population for a prolonged period (years), with comparison of incidence rates of the given disease in groups that differ in exposure levels.


  • (Everitt & Howell, 2005) ⇒ Brian S. Everitt, and D. Howell. (2005). “Encyclopedia of Statistics in Behavioral Science." Wiley. ISBN:9780470860809
    • QUOTE: In a controlled observational cohort study, two groups of subjects are selected from two populations that (hopefully) differ in only one characteristic at the start. The groups of subjects are studied for a specific period and contrasted at the end of the study period. For instance, smokers and nonsmokers are studied for a period of 10 years, and at the end the proportions of smokers and nonsmokers that died in that period are compared. On the other hand, in an intervention study, the subjects are selected from one population with a particular characteristic present; then, immediately after baseline, the total study group is split up into a group that receives the intervention and a group that does not receive that intervention (control group). The comparison of the outcomes of the two groups at the end of the study period is an evaluation of the intervention. For instance, smokers can be divided into those who will be subject to a smoking-cessation program and those who will not be motivated to stop smoking. [1]