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.

Except for retrospective cohorts

Sometimes difficult.

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

Easier to show that cause precedes effect.

More difficult

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

Many staff, large data sets

Long duration

Easier

Concept

Easy to understand

Difficult to understand particularly if case cohort or density case control study

Ethical issues

Major if studying risk factors.

Interruption of study if exposure shown to be harmful.

Need for intermediate analysis.

None since outcome already happened.