Comparative observational studies- Case control study is one of the type of Comparative observational studies.
In contrast with cohort and cross sectional studies, case control studies are usually retrospective. People with the outcome of interest are matched with a control group who do not. Retrospectively the researcher determines which individuals were exposed to the agent or treatment or the prevalence of a variable in each of the study groups. Where the outcome is rare, case-control studies may be the only feasible approach.
As some of the subjects have been deliberately chosen because they have the disease in question case-control studies are much more cost efficient than cohort and cross sectional studies—that is, a higher percentage of cases per study.
Case-control studies determine the relative importance of a predictor variable in relation to the presence or absence of the disease. Case-control studies are retrospective and cannot therefore be used to calculate the relative risk; this a prospective cohort study. Case-control studies can however be used to calculate odds ratios, which in turn, usually approximate to the relative risk.
How to run a case-control study
1. Decide on the research question to be answered.
2.Formulate an hypothesis and then decide what will be measured and how.
3. Specify the characteristics of the study group and decide how to construct a valid control group. Then compare the “exposure” of the two groups to each variable.
Advantages and disadvantages of case-control study
- Good for examining rare outcomes or outcomes with long latency
- Relatively quick to conduct
- Relatively inexpensive
- Requires comparatively few subjects
- Existing records can be used
- Multiple exposures or risk factors can be examined
- Susceptible to recall bias or information bias
- Difficult to validate information
- Control of extraneous variables may be incomplete
- Selection of an appropriate comparison group may be difficult
- Rates of disease in exposed and unexposed individuals cannot be determined
Key points of Case-control studies
• Case-control studies are simple to organise
• Retrospectively compare two groups
• Aim to identify predictors of an outcome
• Permit assessment of the influence of predictors on outcome via calculation of an odds ratio
• Useful for hypothesis generation
• Can only look at one outcome
• Bias is an major problem
Reference: Plast Reconstr Surg. 2010 December ; 126(6): 2234–2242. doi:10.1097/PRS.0b013e3181f44abc