A randomized controlled trial or RCT is a study in which a number of similar people are randomly assigned to 2 (or more) groups to test a treatment, a drug or other intervention. One group (the experimental group) has the intervention being tested, the other (the comparison or control group) has an alternative intervention, a dummy intervention (placebo) or no intervention at all. The groups are followed up to see how effective the experimental intervention was. Outcomes are measured at specific times and any difference in response between the groups is assessed statistically. RCTs are considered to be the most reliable form of scientific evidence that influences healthcare policy and practice because RCTs reduce the likelihood that the observed associations are due to chance or are biased.