About and methodology

General scientific information, not medical advice. It describes what studies found for groups of people. It is not a diagnosis and it gives no dose, plan or advice for any one person.

What this database is

Based on Evidence is a free, open evidence database. For each topic, a grid of intervention against outcome: the certainty of the evidence, the pooled effect with its 95% confidence interval, the number of studies and participants, and the studies behind each cell. Every cell and every study page is free to read, without an account. Nothing is locked or limited.

How a certainty level is made

Certainty answers one question: how confident can we be that the result is close to the truth? It is not the size of the effect and not the number of studies. We use the GRADE way of thinking, with five labels: High, Moderate, Low, Very low and Insufficient. A level reaches this site by one of two routes, and each cell says which:

• GRADE as published. A named systematic review reports its own GRADE certainty. We copy the level and the authors’ wording as written and name the review (with its PubMed ID). We do not re-grade it.
• Platform rules. Where no published rating exists, a rule engine (version shown on each cell) proposes a level from the extracted meta-analysis data. It starts at High for bodies of randomised trials and at Low for non-randomised evidence, and lowers the level for risk of bias (as the review authors report it; we do not judge it ourselves), inconsistency between studies, imprecision (wide intervals, few participants) and signs of publication bias. It never decides indirectness; that is left to a person. It raises the level only when nothing was lowered and the effect is very large.

Nothing is published without a named reviewer. Every level shown here has been signed off by a named person with a written justification, and that name is on the cell. Until then the cell reads “Pending review”: it shows the effect with its 95% confidence interval, the number of studies and participants and the sources with their quotes, but no certainty level. “Insufficient” is a level a reviewer gives when the evidence is too thin to say anything. Wording follows the standard GRADE statements: “results in” for High, “probably” for Moderate, “may” for Low, “the evidence is very uncertain” for Very low. A result that is not clearly different from no difference is described as exactly that, never as “no effect”.

How the numbers are extracted

AI-assisted extraction, reviewed by Maxime De Keyser (MDK Coaching). A language model reads each paper and copies the values it states. Every value is stored with the verbatim sentence it came from and where that sentence sits in the paper; use “Show quote” on a study page to read it. A value without a verifiable quote is left empty. The model is never asked to calculate: any statistic derived from reported values is computed by code and marked as such. Extraction runs twice and disagreements are settled before a record is used.

Retractions and corrections

We check PubMed, Crossref and the Retraction Watch database. A retracted paper stays listed and readable, with a banner at the top, and is not counted in any grade. Corrections and expressions of concern are shown as warnings. See data sources.

Licences and abstracts

Most papers are copyrighted. We show an abstract only where the article’s open licence allows it; for all other papers we show the bibliographic record, any short quote behind an extracted value, and a link to PubMed. Each study page carries a licence badge. Because some open licences exclude commercial use, this site is run without advertising, paid tiers, or supplement and affiliate links.

What this site is not

• General scientific information, not medical advice.
• It is not a substitute for a conversation with a qualified health professional.
• Talk to a qualified professional before changing your diet, supplements, exercise or medication; supplements can interact with medicines.
• AI can make mistakes and sources can be retracted. Check the quote and the paper.
• In an emergency, call 112.

Operator, corrections and contact

MDK Coaching BV, enterprise number BE0779.246.728, Belgium.

The site is hosted by Vercel (pages generated in Frankfurt) and its research data is kept in a Supabase database in Frankfurt. It sets no cookies and runs no analytics; see Privacy.

Found an error in an extracted value, a missing retraction notice or a licence problem? Write to the contact address above.