Which best describes randomized controlled trials (RCTs)?

Randomized controlled trials (RCTs) are characterized by the process of random assignment of participants to either treatment or control groups. This methodological feature is crucial as it helps eliminate bias and ensures that the groups are comparable at the start of the trial. By randomly assigning participants, researchers can more confidently attribute any differences in outcomes directly to the intervention or treatment being tested, rather than to pre-existing differences between the participants.

This approach allows for a more rigorous evaluation of the effectiveness and safety of interventions, making RCTs one of the gold standards in clinical research. Their design strengthens the validity of the study findings, as randomization tends to balance both known and unknown confounding factors across the groups.

Other options describe different types of study designs. Observational studies do not involve intervention or assignment and are focused on observing outcomes and exposures in natural settings. Expert consensus refers to guidelines or recommendations shaped by the opinions of specialists rather than empirical data, and retrospective studies analyze existing data instead of conducting new interventions, which is the opposite of what RCTs do.