What is a key characteristic of a randomized controlled trial (RCT)?

The defining characteristic of a randomized controlled trial (RCT) is that participants are randomly assigned to treatment or control groups. This randomization is what distinguishes an RCT from other types of research studies and is the feature that gives it its name.

Random assignment means that each participant has an equal chance of being placed in either the treatment group (which receives the intervention being tested) or the control group (which receives a placebo or standard treatment). This process eliminates selection bias and ensures that any differences in outcomes between the groups can be attributed to the intervention rather than to pre-existing differences between participants.

The other options describe features that may be present in some RCTs but are not their key defining characteristic:

• Studies conducted in a laboratory setting describes the location, not the design. RCTs can be conducted in hospitals, communities, clinics, or any appropriate setting.
• Researchers blinded to participant groups (blinding) is a valuable methodological feature used in many RCTs, but it is an additional design feature, not the fundamental defining element.
• Participants selected based on specific criteria describes inclusion and exclusion criteria, which apply to many study designs, not just RCTs.