More information on the number of sources and documents we collect
Overton indexes more than 22M documents from more than 2,700+ different policy sources, making it larger than similar systems.
Overton was designed specifically for working with policy rather tracking non-scholarly attention more broadly. The positive side of this trade-off is that we’re able to quickly add and process new policy sources and to do a better job of matching references in free text.
It’s important to note that a “policy source” in this context is a website or domain from which we are collecting documents.
Usually a website (Overton policy source) includes documents from just one organisation, but this varies from country to country.
For example, in the UK a single policy source – gov.uk – hosts documents from all of the government’s departments as well as many government agencies.
Conversely in Australia each government department hosts its own documents, so each one is tracked as a separate policy source.
Policy to policy citations
Uniquely Overton also tracks citations within the policy literature rather than just from policy documents to scholarly articles. There are ~ 10M policy to policy citations in the database. They are kept in a separate index, but are searchable alongside the ~ 28M policy to DOI citations.
This is a core part of our business and is how we’re able to work with government agencies, think tanks and NGOs who don’t always publish in academic books and journals. Our customers often have a mix of output types. For example, think tanks and universities may be publishing both scholarly works and policy briefs or reports.
Looking at coverage in different countries
You can use the number of sources in each country as a very broad indicator of how good coverage is, but if you’re focused on a specific geographical area then the best approach is to combine this datapoint with the volume of policy documents sources produce .
Regular data analyses highlight that government bodies account for around 42% of sources but author 75% of policy documents, reflecting their broader remit, productivity and different publication practices.
Consider this when comparing citation rates between countries and organisation types (you can use Overton policy source taxonomy to unpick those nuances).