Retrospective cohort study
A retrospective cohort study, also called a historic cohort study, is a
Design
The retrospective cohort study compares groups of individuals who are alike in many ways but differ by a certain characteristic (for example, female nurses who smoke and ones who do not smoke) in terms of a particular outcome (such as lung cancer).[2] Data on the relevant events for each individual (the form and time of exposure to a factor, the latent period, and the time of any subsequent occurrence of the outcome) are collected from existing records and can immediately be analyzed[3] to determine the relative risk of the cohort compared to the control group.[4]
This is fundamentally the same methodology as for a prospective cohort study, except that the retrospective study is performed post-hoc, looking back.[3] The prospective study looks forward, enrolling patients unaffected by the outcome and observing them to see whether the outcome has occurred.[3] However, both kinds of cohort studies share the same starting point (considering data from before the occurrence of the outcome). The first objective is still to establish two groups - exposed versus non-exposed - which are then assessed retrospectively to establish the most likely temporal sequence of events leading to the current disease state in both the exposed and unexposed groups.[citation needed]
Retrospective cohort studies require particular caution because errors due to confounding and bias are more common than in prospective studies.[4]
Advantages
Retrospective cohort studies exhibit the benefits of
- They are conducted on a smaller scale.[5]
- They typically require less time to complete.[5]
- They are generally less expensive, because resources are mainly devoted to collecting data.[6]
- They are better for analyzing multiple outcomes.[6]
- In a medical context, they can potentially address rare diseases, which would necessitate extremely large cohorts in prospective studies.[5]
Retrospective studies are especially helpful in addressing diseases of low incidence, since affected people have already been identified so .
Disadvantages
Retrospective studies have disadvantages vis-a-vis prospective studies:
- Some key statistics cannot be measured, and significant biases may affect the selection of controls.[5]
- Researchers cannot control exposure or outcome assessment, and instead must rely on others for accurate recordkeeping.[6] When relying on individual recall of former exposure to risk variables, recall may be inaccurate and subject to biases.[5] It can be very difficult to make accurate comparisons between the exposed and the non-exposed.[6]
- The retrospective aspect may introduce selection bias and mis-classification or information bias.[8] With retrospective studies, the temporal relationship is frequently difficult to assess.[6]
- Retrospective studies may need very large sample sizes for rare outcomes.[6]
Comparison with case-control studies
While retrospective cohort studies try to compare the risk of developing a disease to some already known exposure factors, a
See also
- Case-control study
References
Citations
- ^ "What is epidemiology?" (PDF). 11 March 2019.
- ^ "Definition of historic cohort study - NCI Dictionary of Cancer Terms".
- ^ PMID 12533370.
- ^ a b "Prospective vs. Retrospective Studies". StatsDirect. Retrieved 2 August 2017.
- ^ a b c d e "Retrospective study".
- ^ a b c d e f g Hyde, James N. "Retrospective Cohort Study: Strengths and Weaknesses". Tufts Open Courseware. Tufts University. Archived from the original on 12 May 2017. Retrieved 2 August 2017.
- ^ "4. The epidemiological approach to investigating disease problems". Archived from the original on 2001-05-05.
- ^ https://onlinecourses.science.psu.edu/stat507/node/54
Sources
- This article incorporates U.S. National Cancer Institute.