The Geneva Graduate Institute's Open Access barometer is based on data from the repository and the Unpaywall database. This makes it possible to distinguish between different types of OA articles:
- hybrid OA: articles published open access in "hybrid journals", i.e. journals with both open access and paywall articles.
- gold OA: articles published in 100% open access journals, with or without publication fees. Open access journals without publication fees are called "diamond journals".
- green OA: articles that have not been published as open access, but are available (usually the AAM, author accepted manuscript) in a not-for-profit repository.
- bronze OA: articles that are freely available, but without a Creative Commons licence. Their copyright status is unclear, and the publisher may choose to place them behind a paywall in the future. They are therefore not truly open access.
