Study design
Randomised controlled trial
A study assigning participants to intervention and comparison groups by chance.
What it means
Definition
Randomised controlled trial. A randomised controlled trial is often the strongest design for testing whether an intervention causes an outcome. Its credibility still depends on adequate size, follow-up, blinding, outcome choice and analysis.
What it can tell you
It can show how close the evidence is to a real human health outcome.
What it cannot tell you
It cannot prove that a treatment works in people unless human outcome data are available.
Headline trap
Why this matters in headlines
A small unblinded RCT with a surrogate endpoint may be less decisive than a headline suggests.