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A case control study involves two groups: one with a health issue (Case) and another without (Control), matched by traits like age and gender. The design allows for examination of shared risk factors.

Case control studies are for appropriate for researching associations between exposure(s) and a health outcome.

Requirements:

  • 4-36 months and at least 3 team members with appropriate expertise. 
  • Case control studies should adhere to the STROBE Statement.
  • You will need to obtain ethics approval and informed consent.

How to do a case control study

  1. Develop a hypothesis and aim
  2. Search the literature
    1. You may need assistance from a librarian
  3. Develop the study methodology
    1. Consider target population, sample size, cases, and controls.
  4. Obtain approval 
  5. Obtain informed consent
  6. Write and register the protocol
  7. Collect data
  8. Analyse data
    1. You may need assistance from a biostatistician
  9. Write up the research
  10. Reference your sources
  11. Publish your research

Examples
Iida, M., et al. (2023). Lens thickness in atopic cataract: case-control study. Journal of cataract and refractive surgery, 49(8), 853–857. 
Logjes, R. J. H., et al. (2022). Robin Sequence: 5-Year Speech Outcomes-A Case-Control Study. Plastic and reconstructive surgery, 150(2), 479e–481e.

Recommended resources:

Medmastery. (2023). How to perform a case control study.

A case-cohort study is a type of observational study that combines features of both case-control and cohort studies. It is useful for studying rare outcomes while maintaining the advantages of a cohort design.

Case-cohort studies can be more efficient than full cohort studies (fewer participants are followed long-term), but they involve complex statistical analysis.

Requirements:

  • 1-5 years and 3-10 team members with appropriate expertise. 
  • Case-cohort studies should adhere to the STROBE Statement.
  • You will need to obtain ethics approval and informed consent.

How to do a case-cohort study

  1. Develop a hypothesis and aim
  2. Search the literature
    1. You may need assistance from a librarian
  3. Develop the study methodology
    1. Consider target population, sample size, cases, and controls.
    2. Select a sub-cohort
  4. Obtain approval 
  5. Obtain informed consent
  6. Write and register the protocol
  7. Collect data
  8. Analyse data
    1. You may need assistance from a biostatistician
  9. Write up the research
  10. Reference your sources
  11. Publish your research

Examples
Kulathinal, S., et al. (2007). Case-cohort design in practice - experiences from the MORGAM Project. Epidemiologic perspectives & innovations, 4, 15.
Winquist, A., et al. (2023). Case-Cohort Study of the Association between PFAS and Selected Cancers among Participants in the American Cancer Society's Cancer Prevention Study II LifeLink Cohort. Environmental health perspectives, 131(12), 127007. 

Recommended resources:

Medical Basic Science. (2021). Nested case control vs case cohort studies.

A nested case-control study is a type of case-control study conducted within a predefined cohort. It is particularly useful for reducing selection bias and improving efficiency when studying rare outcomes.

Requirements:

  • 1-5 years and 3-10 team members with appropriate expertise. 
  • Nested case-control studies should adhere to the STROBE Statement.
  • You will need to obtain ethics approval and informed consent.

How to do a nested case-control study

  1. Develop a hypothesis and aim
  2. Search the literature
    1. You may need assistance from a librarian
  3. Develop the study methodology
    1. Select an existing cohort study
    2. Identify individuals from within the cohort who developed the outcome
    3. Controls should come from the same cohort but have not developed the outcome at the time each case is diagnosed
  4. Obtain approval 
  5. Obtain informed consent
  6. Write and register the protocol
  7. Collect data
  8. Analyse data
    1. You may need assistance from a biostatistician
  9. Write up the research
  10. Reference your sources
  11. Publish your research

Examples
Dehara, M., et al. (2022). Reproductive and hormonal risk factors for sarcoidosis: a nested case-control study. BMC pulmonary medicine, 22(1), 43. 
Moltubak, E., et al. (2024). Validation of the Appendicitis Inflammatory Response (AIR) score during pregnancy: A nested case-control study. Academic emergency medicine, 31(9), 894–902. 

Recommended resources:

Medical Basic Science. (2021). Nested case control vs case cohort studies.

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