Table 1 Advantages and disadvantages of randomized control trials and observational cohort studies

Randomized controlled trial

Unbiased randomization

(Hence baseline characteristics of the groups are likely to be as similar as possible)

Differences in outcome between groups can be attributed to the intervention

Facilitates statistical analysis

Maybe time consuming and can be expensive

Potential ethical issues

Volunteer bias

Observational cohort study

Best way to ascertain both incidence and natural history

Useful to investigate multiple outcomes and rare diseases

Useful when randomization is not possible

Liable for bias

Cannot establish a causative relationship between exposure to risk factor and developing an outcome