Preprint data is currently updated on a weekly schedule - details of these releases can be found in
release_date refers to the date on which data was collected, and
sample_date the cut-off point for preprints to be included based on their posting date.
Note that this dataset is not exhaustive, but aims to collate information from some of the main sources of preprint metadata.
The process for collecting preprint metadata is documented fully here. In general terms, preprint metadata are harvested from four main sources:
Crossref (using the rcrossref package). All records with the
typefield defined as
posted-contentare harvested, as well as records from SSRN (where the
typefield is instead defined as
journal-article). Preprint records are then matched to known preprint repositories based on
DataCite (using the rdatacite package). All records with the
resourceTypefield defined as
Preprintare harvested. Preprint records are matched to known preprint repositories based on
arXiv (using the aRxiv package). Records are harvested by searching directly for COVID-19 related keywords in titles or abstracts using the built-in search functionality of the arXiv API.
RePEc (using the oai package)). All record types are initally harvested, and subsequently filtered for those with the
Typefield defined as
For all sources, preprints are classified as being related to
COVID-19 on the basis of keyword matches in their titles or abstracts
(where available). The search string is defined as:
coronavirus OR covid-19 OR sars-cov OR ncov-2019 OR 2019-ncov OR hcov-19 OR sars-2.
In some cases, multiple preprint metadata records are registered for a single preprint (e.g. ChemRxiv registers a new Crossref record for each new version of a preprint). In these cases, only the earliest posted version is included in this dataset. Additionally, some preprints are deposited to multiple preprint repositories - in these cases all preprint records are included.