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Research Guides@Tufts

Study Designs in the Health Sciences

An introduction to the main features and uses of study designs popular and unique to medicine and the health sciences.

Retrospective Cohort Study

What is a retrospective cohort study?

"The distinguishing feature of a retrospective cohort study is that the investigators conceive the study and begin identifying and enrolling subjects after outcomes have already occurred....[this type of study is] very efficient for studying rare or unusual exposures, but there are many potential problems here. Sometimes exposure status is not clear when it is necessary to go back in time and use whatever data is available, especially because the data being used was not designed to answer a health question."[1]

Why use this type of study?

  • cheaper and quicker to run as the data have already been collected [2]
  • reduction in  bias because the outcome of current interest was not the original reason for the data to be collected; however "because the cohort was originally constructed for another purpose it is unlikely that all the relevant information will have been rigorously collected"[2]

References

  1.  Boston University School of Public Health. Prospective and Retrospective Cohort Studies. https://sphweb.bumc.bu.edu/otlt/mph-modules/ep/ep713_analyticoverview/ep713_analyticoverview3.html. Access November 6, 2024
  2. Mann CJ. Observational research methods. Research design II: cohort, cross sectional, and case-control studies. Emerg Med J. 2003 Jan;20(1):54-60. doi: 10.1136/emj.20.1.54. PMID: 12533370; PMCID: PMC1726024.

 

Example

New-onset obstructive airway disease following COVID-19: a multicenter retrospective cohort study. 

Chuang MH, Hsu W, Tsai YW, Hsu WH, Wu JY, Liu TH, Huang PY, Lai CC.

BMC medicine, 22(1), 360. https://doi.org/10.1186/s12916-024-03589-4


Background: The study assessed the association between COVID-19 and new-onset obstructive airway diseases, including asthma, chronic obstructive pulmonary disease, and bronchiectasis among vaccinated individuals recovering from COVID-19 during the Omicron wave.

Methods: This multicenter retrospective cohort study comprised 549,606 individuals from the U.S. Collaborative Network of TriNetX database, from January 8, 2022, to January 17, 2024. The hazard of new-onset obstructive airway diseases between COVID-19 and no-COVID-19 groups were compared following propensity score matching using the Kaplan-Meier method and Cox proportional hazards model.

Results: After propensity score matching, each group contained 274,803 participants. Patients with COVID-19 exhibited a higher risk of developing new-onset asthma than that of individuals without COVID-19 (adjusted hazard ratio (aHR), 1.27; 95% CI, 1.22-1.33; p < 0.001). Stratified analyses by age, SARS-CoV-2 variant, vaccination status, and infection status consistently supported this association. Non-hospitalized individuals with COVID-19 demonstrated a higher risk of new-onset asthma (aHR, 1.27; 95% CI, 1.22-1.33; p < 0.001); however, no significant differences were observed in hospitalized and critically ill groups. The study also identified an increased risk of subsequent bronchiectasis following COVID-19 (aHR, 1.30; 95% CI, 1.13-1.50; p < 0.001). In contrast, there was no significant difference in the hazard of chronic obstructive pulmonary disease between the groups (aHR, 1.00; 95% CI, 0.95-1.06; p = 0.994).

Conclusion: This study offers convincing evidence of the association between COVID-19 and the subsequent onset of asthma and bronchiectasis. It underscores the need for a multidisciplinary approach to post-COVID-19 care, with a particular focus on respiratory health.