Advantages and disadvantages of cohort and case control studies

Many text books have described advantages and disadvantages of cohort and case control studies. The following table summarises useful comments.

	Cohort studies	Case control studies
Suited for rare diseases	No	Yes since starting with a set of cases
Suited for rare exposures	Yes since starting with exposure status	No
Allows for studying several exposures	Difficult but examples exists (Framingham study)	Yes
Allows for studying several outcomes	Yes	No
Disease status easy to ascertain	Sometimes difficult	Easier since starting point of the study
Exposure status easier to ascertain	Yes since starting point of the study.	Sometimes difficult.
	Except for retrospective cohorts	Information biases.
Allows computation of risk and rates	Yes	No
Allows computation of effect	Computation of risk ratio and rate ratio	Estimation of risk ratio, rate ratio from odds ratio
Allows studying natural history of disease	Yes	More difficult
	Easier to show that cause precedes effect.	Temporality between cause and effect difficult to establish
Based on existing data sources	Difficult	Yes but access to information sometimes difficult
Easiness to find a reference group	Usually not difficult to identify an unexposed population	No
		Major potential biases when selecting a control group
Sample size	Large	Small
Cost	Elevated except if retrospective cohorts	Smaller
Time required	Long, sometimes very long except if retrospective cohorts	Shorter
Follow up	Difficult, loss to follow up	No follow up
Logistics	Heavy	Easier
	Many staff, large data sets
	Long duration
Concept	Easy to understand	Difficult to understand particularly if case cohort or density case control study
Ethical issues	Major if studying risk factors.	None since outcome already happened.
	Interruption of study if exposure shown to be harmful.
	Need for intermediate analysis.

FEM PAGE CONTRIBUTORS 2007

Editors

Masja Straetemans

Original Authors

Alain Moren

Jean Claude Desenclos

Marta Valenciano

Arnold Bosman

Contributors

Arnold Bosman

Masja Straetemans