Keywords: cohort, longitudinal study, follow-up. These are studies that may point to statistical associations between exposure and outcome that need other models to prove the casualty of these associations. They have as main biases those of selection, memory and information. However, they are often long and therefore expensive studies. These types of studies have as advantages the possibility of measuring several exposure factors and outcomes, both primary and secondary, for both relatively frequent outcomes and rare exposure factors. Cohort studies may be retrospective or prospective, and both assume that the researcher will follow a population over time to seek a possible association between exposure (s) and outcome(s). In health sciences, the epidemiological method can be divided into descriptive and analytical epidemiology and the latter being divided into observational (cross-sectional study, case-control study and cohort study) and experimental studies. VIISchool of Application, Federal University of Acre, Rio Branco, Acre, Brazil VICenter for Health and Sports Sciences, Federal University of Acre, Rio Branco, Acre, Brazil VStricto Sensu Graduate Program in Health Science in the Western Amazon, Federal University of Acre, Rio Branco, Acre, Brazil IVNational Institute of Science and Technology EpiAmo / Rondônia IIICenter of Tropical Medicine of Rondônia, Porto Velho, Rondônia, Brazil IIDepartment of Medicine, São Lucas University Center, Porto Velho, Rondônia, Brazil IInstitute of Biomedical Sciences, University of São Paulo, Monte Negro, Rondônia, Brazil Luís Marcelo Aranha Camargo I, II, III, IV, V Romeu Paulo Martins Silva V, VI Dionatas Ulises de Oliveira Meneguetti V, VII Research methodology topics: Cohort studies or prospective and retrospective cohort studies

prone to the bias of change in methods over time.

prone to attrition bias (compensate by using person-time methods).

may uncover unanticipated associations with outcome.

yields true incidence rates and relative risks.

The following notes relate cohort to case-control studies: related methods are risk (retrospective), chi-square 2 by 2 test, Fisher's exact test, exact confidence interval for odds ratio, odds ratio meta-analysis and conditional logistic regression.Ĭohort studies are usually but not exclusively prospective, the opposite is true for case-control studies.controls are selected on the basis of not having the outcome.The following notes relate case-control to cohort studies: Prospective investigation is required to make precise estimates of either the incidence of an outcome or the relative risk of an outcome based on exposure.Ĭase-Control studies are usually but not exclusively retrospective, the opposite is true for cohort studies. You should take special care to avoid sources of bias and confounding in retrospective studies. In retrospective studies the odds ratio provides an estimate of relative risk. If the outcome of interest is uncommon, however, the size of prospective investigation required to estimate relative risk is often too large to be feasible. For this reason, retrospective investigations are often criticised. Most sources of error due to confounding and bias are more common in retrospective studies than in prospective studies. Many valuable case-control studies, such as Lane and Claypon's 1926 investigation of risk factors for breast cancer, were retrospective investigations. Prospective studies usually have fewer potential sources of bias and confounding than retrospective studies.Ī retrospective study looks backwards and examines exposures to suspected risk or protection factors in relation to an outcome that is established at the start of the study. All efforts should be made to avoid sources of bias such as the loss of individuals to follow up during the study. The outcome of interest should be common otherwise, the number of outcomes observed will be too small to be statistically meaningful (indistinguishable from those that may have arisen by chance). The study usually involves taking a cohort of subjects and watching them over a long period.

Retrospective StudiesĪ prospective study watches for outcomes, such as the development of a disease, during the study period and relates this to other factors such as suspected risk or protection factor(s). Open topic with navigation Prospective vs. Prospective, Retrospective, Case-control, Cohort Studies - StatsDirect

Retrospective cohort vs case control