On This Page:
A case-control study is a research method where two groups of people are compared – those with the condition (cases) and those without (controls). By looking at their past, researchers try to identify what factors might have contributed to the condition in the ‘case’ group.
Definition
A case-control study looks at people who already have a certain condition (cases) and people who don’t (controls). By comparing these two groups, researchers try to figure out what might have caused the condition. They look into the past to find clues, like habits or experiences, that are different between the two groups.
The “cases” are the individuals with the disease or condition under study, and the “controls” are similar individuals without the disease or condition of interest.
The controls should have similar characteristics (i.e., age, sex, demographic, health status) to the cases to mitigate the effects of confounding variables.
Case-control studies identify any associations between an exposure and an outcome and help researchers form hypotheses about a particular population.
Researchers will first identify the two groups, and then look back in time to investigate which subjects in each group were exposed to the condition.
If the exposure is found more commonly in the cases than the controls, the researcher can hypothesize that the exposure may be linked to the outcome of interest.
Figure: Schematic diagram of case-control study design. Kenneth F. Schulz and David A. Grimes (2002) Case-control studies: research in reverse. The Lancet Volume 359, Issue 9304, 431 – 434
Advantages
Quick, inexpensive, and simple
Because these studies use already existing data and do not require any follow-up with subjects, they tend to be quicker and cheaper than other types of research. Case-control studies also do not require large sample sizes.
Beneficial for studying rare diseases
Researchers in case-control studies start with a population of people known to have the target disease instead of following a population and waiting to see who develops it. This enables researchers to identify current cases and enroll a sufficient number of patients with a particular rare disease.
Useful for preliminary research
Case-control studies are beneficial for an initial investigation of a suspected risk factor for a condition. The information obtained from cross-sectional studies then enables researchers to conduct further data analyses to explore any relationships in more depth.
Limitations
Subject to recall bias
Participants might be unable to remember when they were exposed or omit other details that are important for the study. In addition, those with the outcome are more likely to recall and report exposures more clearly than those without the outcome.
Difficulty finding a suitable control group
It is important that the case group and the control group have almost the same characteristics, such as age, gender, demographics, and health status.
Forming an accurate control group can be challenging, so sometimes researchers enroll multiple control groups to bolster the strength of the case-control study.
Do not demonstrate causation
Case-control studies may prove an association between exposures and outcomes, but they can not demonstrate causation.
Examples
A case-control study is an observational study where researchers analyzed two groups of people (cases and controls) to look at factors associated with particular diseases or outcomes.
Below are some examples of case-control studies:
- Investigating the impact of exposure to daylight on the health of office workers (Boubekri et al., 2014).
- Comparing serum vitamin D levels in individuals who experience migraine headaches with their matched controls (Togha et al., 2018).
- Analyzing correlations between parental smoking and childhood asthma (Strachan and Cook, 1998).
- Studying the relationship between elevated concentrations of homocysteine and an increased risk of vascular diseases (Ford et al., 2002).
- Assessing the magnitude of the association between Helicobacter pylori and the incidence of gastric cancer (Helicobacter and Cancer Collaborative Group, 2001).
- Evaluating the association between breast cancer risk and saturated fat intake in postmenopausal women (Howe et al., 1990).
Frequently asked questions
1. What’s the difference between a case-control study and a cross-sectional study?
Case-control studies are different from cross-sectional studies in that case-control studies compare groups retrospectively while cross-sectional studies analyze information about a population at a specific point in time.
In cross-sectional studies, researchers are simply examining a group of participants and depicting what already exists in the population.
2. What’s the difference between a case-control study and a longitudinal study?
Case-control studies compare groups retrospectively, while longitudinal studies can compare groups either retrospectively or prospectively.
In a longitudinal study, researchers monitor a population over an extended period of time, and they can be used to study developmental shifts and understand how certain things change as we age.
In addition, case-control studies look at a single subject or a single case, whereas longitudinal studies can be conducted on a large group of subjects.
3. What’s the difference between a case-control study and a retrospective cohort study?
Case-control studies are retrospective as researchers begin with an outcome and trace backward to investigate exposure; however, they differ from retrospective cohort studies.
In a retrospective cohort study, researchers examine a group before any of the subjects have developed the disease, then examine any factors that differed between the individuals who developed the condition and those who did not.
Thus, the outcome is measured after exposure in retrospective cohort studies, whereas the outcome is measured before the exposure in case-control studies.
References
Boubekri, M., Cheung, I., Reid, K., Wang, C., & Zee, P. (2014). Impact of windows and daylight exposure on overall health and sleep quality of office workers: a case-control pilot study. Journal of Clinical Sleep Medicine: JCSM: Official Publication of the American Academy of Sleep Medicine, 10 (6), 603-611.
Ford, E. S., Smith, S. J., Stroup, D. F., Steinberg, K. K., Mueller, P. W., & Thacker, S. B. (2002). Homocyst (e) ine and cardiovascular disease: a systematic review of the evidence with special emphasis on case-control studies and nested case-control studies. International journal of epidemiology, 31 (1), 59-70.
Helicobacter and Cancer Collaborative Group. (2001). Gastric cancer and Helicobacter pylori: a combined analysis of 12 case control studies nested within prospective cohorts. Gut, 49 (3), 347-353.
Howe, G. R., Hirohata, T., Hislop, T. G., Iscovich, J. M., Yuan, J. M., Katsouyanni, K., … & Shunzhang, Y. (1990). Dietary factors and risk of breast cancer: combined analysis of 12 case—control studies. JNCI: Journal of the National Cancer Institute, 82 (7), 561-569.
Lewallen, S., & Courtright, P. (1998). Epidemiology in practice: case-control studies. Community eye health, 11 (28), 57–58.
Strachan, D. P., & Cook, D. G. (1998). Parental smoking and childhood asthma: longitudinal and case-control studies. Thorax, 53 (3), 204-212.
Tenny, S., Kerndt, C. C., & Hoffman, M. R. (2021). Case Control Studies. In StatPearls. StatPearls Publishing.
Togha, M., Razeghi Jahromi, S., Ghorbani, Z., Martami, F., & Seifishahpar, M. (2018). Serum Vitamin D Status in a Group of Migraine Patients Compared With Healthy Controls: A Case-Control Study. Headache, 58 (10), 1530-1540.
Further Information
