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Table 2 Definition of access categories at the paper level
| Category | Definition | Article processing fees | Subscription fees | Embargo |
|---|---|---|---|---|
| Gold OA article (no APC) | Article published in gold OA journal website when published; instantly available on journal website when published | No | No | No |
| Gold OA article (with APC) | Article published in gold OA journal; instantly available on journal website when published | Yes | No | No |
| Delayed OA article | Free article published in delayed OA or subscription journal with delayed OA option | No | Yes | Yes |
| Hybrid article | Free article published in a subscription journal | Yes | Yes | No |
| Green OA article | Articles in subscription or hybrid journals which have been self-archived by the author or affiliated institution to provide free access | No | No | No |
| Other free access | Free article in subscription journal or journal for which the status is unknown | Unknown | Sometimes | Sometimes |
| Toll access | Article that can only be accessed through a subscription or pay-per-view model and has not been self-archived | No | Yes | Yes |
| Paper status unknown | Article for which the access status could not be determined | Unknown | Unknown | Unknown |
