Evidence methodology
The hierarchy of evidence
| Level | Source type | What it shows |
|---|---|---|
| 1 | Guidelines from WHO, U.S. federal agencies (USPSTF, CDC, HHS) and professional societies | Consensus recommendations based on systematic review |
| 2 | Systematic reviews and meta-analyses, including Cochrane | The pooled result of many studies |
| 3 | Randomized controlled trials | The causal effect of an intervention |
| 4 | Prospective cohort studies | How habits relate to health over time |
| 5 | Case-control and cross-sectional studies | Possible risk factors |
| 6 | Small, pilot and laboratory studies | Hypotheses and mechanisms |
How we check sources
- Search. PubMed, Google Scholar, the Cochrane Library, WHO and U.S. agency websites, and professional societies. We prefer journals indexed in Scopus and Web of Science.
- DOI verification. Every DOI is automatically checked against Crossref: title, authors, journal and year must match. If a DOI cannot be confirmed, the site will not build.
- Reading. We look at sample size, study design, duration, funding and the limitations the authors report.
- Numbers. We cite specific figures from the source and make clear whether a risk is relative or absolute.
- Context. We explain who a recommendation may not suit and add a "When to see a doctor" section.
U.S. adaptation
The English edition is adapted for readers in the United States: we reference the Dietary Guidelines for Americans, the Physical Activity Guidelines for Americans, CDC and USPSTF recommendations, U.S. units (ounces, pounds, °F) and U.S. emergency numbers (911 and the 988 Suicide & Crisis Lifeline).
Quizzes and calculators
We only use validated questionnaires whose terms allow free use (PHQ-9, GAD-7, AUDIT, IPAQ and others) and clearly label editorial tools that are not validated. Results are a self-check, not a diagnosis.
What we never do
- Give individual medical advice or recommend doses of medicines or supplements.
- Cite studies we cannot verify.
- Present observational data as proof of cause.
- Sell supplements or publish hidden advertising.
Frequently asked questions
Do you use AI?
We use AI tools to help search, structure and draft. Every scientific source is checked, every DOI is verified against Crossref, and the editorial team is responsible for the content.
How often are articles updated?
At least once a year, or sooner when important new studies or guidelines are published. The update date is shown on every article.
See also: editorial policy, source library, glossary.