How we grade evidence

Every article carries a grade from A to E. It tells you how much weight the evidence can carry, not whether the news is good or bad.

• A · Strong: large randomized trials or meta-analyses in people, with hard outcomes.
• B · Good: randomized trials in people with smaller samples, shorter follow-up or lab markers.
• C · Moderate: well-done observational studies in people.
• D · Limited: small or early studies in people.
• E · Very limited: studies in cells or animals only.

Draft: the editors will replace this table with the final criteria.