Sources and dates
How each figure on this site is found, checked, dated and corrected.
A publication built on numbers owes readers an account of where the numbers come from. This page describes the rules the editors follow for every figure, and what happens when a source changes or a mistake turns up.
What counts as a source
A figure is used only if the editors opened a page that shows it. The preferred sources are public health agencies and research institutes (for example the US Centers for Disease Control and Prevention, the National Cancer Institute, the National Institutes of Health, the World Health Organization and the UK National Health Service), reports of the US Surgeon General, systematic reviews such as those from Cochrane, and peer-reviewed papers. Press releases, product pages, forums and social media are not used for figures. When a figure comes from a single survey or trial, the page says so.
The figure at the top of each page
Each topic page opens with one headline figure, shown large, followed by a sentence saying what it measures, the name of the publisher and document, and the year the data or page refers to. The plate links to the exact page that was opened. When no figure on a topic could be matched to an opened source, the plate says so instead of showing an estimate. The editors do not calculate their own statistics, do not round a figure in a way that changes its meaning, and do not combine figures from different surveys into one.
Dates and how guidance ages
Every figure is tied to the year of the data. A survey figure from one year can differ from the next year's, and a guideline can be replaced. Each page shows the date the editors last checked it against its sources, which is the date the sources were opened, not the date the underlying data were collected. Where a source page has moved or been replaced, the newer page is used and the older figure is dropped unless it is clearly labelled as historical.
Health content
Pages on medicines, vaping and symptoms report what authoritative bodies state and no more. They do not recommend that a reader start, stop or change a medicine, and they point to a doctor, nurse or pharmacist for individual questions. If a topic has weak or conflicting evidence, the page says that plainly.
Corrections
If a figure does not match its source, or a source has been updated, write to the editors through the contact page with the page address and, if you can, the link to the newer source. Corrections are made on the page itself and the check date changes. For a tour of the evidence, the methods comparison and the recovery timeline are good places to begin.
The short version
No figure without a source the editors opened, no estimate in place of a missing number, and a visible date on everything. Mistakes are corrected on the page.