Sources policy

How we rank sources

Every source we cite is labelled with one of three types, and the label appears next to the citation so you can weigh it yourself.

• Primary — the original record. Municipal archives, contemporaneous accounts, expedition journals, court documents, original photographs, government data.
• Peer-reviewed — research published in a journal with peer review, or presented to a scholarly body.
• Secondary — reputable reporting or scholarship that synthesises primary material. Useful for context; never sufficient on its own.

The minimum

At least one primary or peer-reviewed source is required for every investigation. A story supported only by secondary sources does not run, regardless of how many secondary sources agree — agreement among aggregators is frequently just one error copied repeatedly.

Following citations to their origin

Where a widely repeated figure or quotation traces to a single source, we say so. A claim repeated in fifty places that originates in one unverified account is a one-source claim, and we treat it as one.

Paywalls and availability

We link to sources whether or not they are freely accessible, and prefer open-access versions where a legitimate one exists. Where a source is offline — an archive holding, for instance — we describe it precisely enough to be located.