A randomized controlled trial (RCT) is a type of scientific experiment used to control factors not under direct experimental control. It is a study design that randomly assigns participants into an experimental group or a control group. In an RCT, the population receiving the program or policy intervention is chosen at random from the eligible population, and a control group is also chosen at random from the same eligible population. The experimental group receives the intervention being tested, while the control group receives either no intervention or an alternative (conventional) treatment. The two groups are then followed up to see if there are any differences between them in outcome. The only expected difference between the control and experimental groups in an RCT is the outcome variable being studied. RCTs are often blinded so that participants and doctors, nurses, or researchers do not know what treatment each participant is receiving, further minimizing bias. RCTs are considered the gold standard for clinical trials because they provide compelling evidence that the study treatment causes an effect on human health.
Some advantages of RCTs include good randomization that will "wash out" any population bias, easier blinding/masking than observational studies, results that can be analyzed with well-known statistical tools, and populations of participating individuals that are clearly identified. However, RCTs can be expensive in terms of time and money, and volunteer biases may occur, meaning that the population that participates may not be representative of the whole. Loss to follow-up attributed to treatment is also a disadvantage of RCTs.
When designing an RCT, researchers must carefully select the population, the interventions to be compared, and the outcomes of interest. Once these are defined, the number of participants needed to reliably determine if such a relationship exists is calculated (power calculation). RCTs can be analyzed by intention-to-treat analysis (ITT), per protocol, or other variations, with ITT often regarded as the least biased. All RCTs should have pre-specified primary outcomes, should be registered with a clinical trials database, and should have appropriate ethical approvals.
In summary, an RCT is a study design that randomly assigns participants into an experimental group or a control group to measure the effectiveness of a new intervention or treatment. It is considered the gold standard for clinical trials because it provides compelling evidence that the study treatment causes an effect on human health.
