Randomized Controlled Trial


A Randomized Controlled Trial (RCT) is a study design that randomly assigns participants into either an experimental group or a control group. As the study is conducted, the only expected difference between the control and experimental groups is the outcome variable being studied.
Generally, in a randomized controlled trial, study participants are randomly assigned to one of two groups: the experimental group receiving the intervention that is being tested and a comparison group (controls) which receives a conventional treatment or placebo. These groups are then followed prospectively to assess the effectiveness of the intervention compared with the standard or placebo treatment.
Randomized controlled trials are the most rigorous way of determining whether a cause-effect relation exists between treatment and outcome and for assessing the cost effectiveness of a treatment.
Important Features
  • Random allocation of participants into an intervention group and control group
  • Patients and trialists should remain unaware of which treatment was given until the study is completed
  • Both intervention and control groups are treated identically except for the experimental treatment


  • Good randomization will remove any population bias
  • Easier to blind/mask than observational studies
  • Results can be analyzed with well-known statistical tools
  • Populations of participating individuals are clearly identified


  • Expensive in terms of time and money
  • Volunteer biases: the population that participates may not be representative of the whole
  • Does not reveal causation
  • Loss to follow-up attributed to treatment

Related Terms
Case Control Study



General outline of a two armed randomized controlled trial: