How we grade evidence
Every article and study page carries one of five labels, listed here strongest first. The order is a guide and not a strict ranking, because a preprint can also be an RCT.
A label tells you what kind of evidence you’re reading, not whether the study is good. A careless trial can show less than a careful small study, so the article also tells you how many people took part and who they were.
- Evidence: Meta-analysis
Pools many studies on the same question.
- Evidence: RCT
One trial, with people put into groups at random.
- Evidence: Small study
Real data from few people or without random groups. A hint, not an answer.
- Evidence: Preprint
Posted before peer review. Treat it as provisional.
- Evidence: Opinion
An argument or expert view, with no new data.