cohort studies
Cohort studies are longitudinal studies, where the research participants are repeatedly observed over a long period. Cohorts or participants who share a common strait, e.g., occupation, are recruited and tracked over time. Through the follow-up period, few of the cohorts would have been exposed to a specific risk factor, thereby computing the outcomes over the period. The impact of this variable can be researched. They are, therefore, valuable epidemiological parameters to assess the influence of factors in the disease process. A cohort study monitors people as groups either exposed to a factor or not exposed over some time and subsequently appraises the occurrence of an outcome. Due to this technicality, cohort studies are favourable to study incidence, etiologies, natural history and prognosis. These studies allow estimating the incidence rate (IR), cumulative incidence (CI), relative risk (RR), and hazard ratio (HR). However, it is not possible to unambiguously establish causality. 1,2
Figure: Graphical representation of the timeline in a prospective vs a retrospective cohort study design [1].They can be either prospective or retrospective in methodology. A prospective cohort study design is categorized superior to retrospective since it is possible to measure and control the outcome, predictor, and confounding variables in a superior way. 1,2 Susceptible to loss to follow-up compared with cross-sectional studies, confound variables are the major challenge in the analyzing the data, Information and recall bias and less control over variables, are some of the disadvantages in cohort studies.3
References
1. Wang X, Kattan MW. Cohort Studies: Design, Analysis, and Reporting. Chest. 2020 Jul;158(1S):S72-S78.
2. Barrett D, Noble H What are cohort studies? Evidence-Based Nursing 2019;22:95-96.
3. Song JW, Chung KC. Observational studies: cohort and case-control studies. PlastReconstr Surg. 2010;126(6):2234-2242.