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National Information Center on Health Services Research and Health Care Technology (NICHSR)

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Introduction to Health Services Research : A Self-Study Course

Module 6: Basic Components of a Study (Page 7 of 11)

Surveys | Cohort Studies | Case-Control Studies | Randomized Clinical Trials

Strengths and Pitfalls: Case-Control Studies

Case-control studies differ from cohort studies in terms of time. Whereas cohort studies follow people over time without knowing the results, case-control studies begin with the outcomes.

These studies start with two similar groups of people. One group (cases) has a disease and the other (controls) is healthy.

Researchers choose people with a particular result (the cases), such as lung cancer, and people similar to the cases who do not have lung cancer (the controls). The researchers then interview the groups or check their records to ascertain what different experiences they had. They compare the odds of having an experience with the outcome to the odds of having an experience without the outcome. Researchers want to know what happened in the past to give such different results.

For example, are people with lung cancer more likely to be smokers than those without lung cancer? Are women with term births more likely to have prenatal care than women with premature births?

Case control studies tell researchers about the different experiences people have that may be related to a particular condition. However, the odds of having one experience compared to other(s) for sick and healthy people varies.

Advantages

Case-control studies offer many benefits to researchers. They are relatively fast and cheap compared to cohort studies and can study multiple exposures. They are very useful for rare diseases that require many years to develop and many people to observe in order to find them.

Disadvantages

However, there are many pitfalls. Researchers must be very cautious when they choose the control group. Controls must be very similar to the cases except for the outcome. Cases & controls may be different in more ways than health! Cases are more likely to remember past experiences than the healthy controls. It is difficult to provide unbiased measurements of exposure in case-control studies.

Discussion Questions

  1. What is the key difference between a cohort study and a case-control study? Why is it necessary to be able to articulate this difference?
  2. What are the search terms that you might use to extract this kind of study when searching using PubMed?
  3. Many Americans are overweight or even obese. The linked search contains one example of a search where case-control studies are used to reduce body mass. What can you learn about health services research by examining the citations that show up in the search? For example, can you find other terms related to studies such as Sensitivity and Specificity or Retrospective Studies as you examine the MeSH headings?
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