What is Case Control Study – ENT Theory Question
Case Control Study is a study that compares patients who have a disease (cases) with patients who do not have the disease (controls), and looks back retrospectively to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between the risk factor and the disease.
The goal is to retrospectively determine the exposure to the risk factor of interest from each of the two groups of individuals: cases and controls. Case control studies are also known as “retrospective studies”.
Types of Study Designs
Observational – include case report, case series, case control study, cohort study Interventional – Randomised control studies, non-randomised control studies
Case Control Study​1–3​
- Observational/ Analytical study
- Generally retrospective = “backward looking” study design
- Effect to Cause
- Begins with the effect/ disease condition, and the investigator goes back in time to try and identify any factor associated with the condition
- A similar group of patients with matched characteristics apart from the disease/effect in question, is taken as the control = CONTROL GROUP
- Control group should be closely matched with the Case group
Go back in time to see how many patients presently with the disease, have been exposed to the factor
Once the values of the above are obtained, Odd’s ratio is obtained
2 x 2 contingency table in a case control study
| Suspected risk factor “Exposure” | Cases (Disease present) | Controls (Disease absent) |
| Present | a | b |
| Absent | c | d |
| a + c | b +d |
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