- 7.1Case-control studies are observational studies that are conducted in three basic steps:
Identify people who have a specific disease or condition
Identify a comparison group of people who do not have this condition
Determine the proportion of each group who had a previous exposure
- 7.2To increase the chance of obtaining valid associations in case-control studies:
Cases should be selected using a specific definition of the disease.
Controls should be selected from the same underlying population as the cases.
Nested case control studies select cases and controls from a unified population.
Matching may be performed to increase similarity between cases and controls.
A steep increase in study power is achieved until about 3–4 controls per case.
- 7.3Analysis of case-control data
The odds ratio is the primary measure of association in case-control studies.
Odds ratios approximate relative risks when the disease outcome is rare.
- 7.4Advantages of case-control studies include:
Useful for studying rare diseases
Can efficiently determine associations using relatively few study participants
Can evaluate multiple risk factors for a disease outcome
- 7.5Limitations of case-control studies include:
Confounding characteristics other than the exposure of interest may bias observed associations with disease
Valid measurements of previous exposures must be obtained in retrospect
Study design prohibits direct calculation of the incidence of disease