Q. What is a CID?

Citation Identifiers (CIDs) are being adopted by some publishers in the place of traditional page numbers for online published documents. Use of CIDs can help provide additional information about the source and are useful for journals that immediately publish articles after review and editing, rather than being published at the same time with other articles as part of an issue. Rather, an issue starts and ends with a time-period set for their publishing schedule. For example, a quarterly publication might have an issue encompass a three month period, but immediately publish articles once they are ready. CIDs do not replace DOIs. Both should be used in a citation, when present.

Within the six digits of a CID are two digit pairs that provide additional information about the source:

1. The first two digits indicates the issue number within the journal volume (a volume typically being a one year time period)
2. The second two digits indicate the type of article OR subject area. This can vary from publication to publication.
3. The third digit indicates which article number it is for the issue

For example, if we had a CID that read 017001 the 01 indicates it is in the first issue, the 70 indicates it is a research article, and the 01 indicates it was the first article in that issue.

If there is a CID followed by a dash and another number, that number after the dash indicates the PDF page number for the article (for example, 017001-2 would mean the second page of the article). As of writing this FAQ CIDs with page numbers are discouraged, though they may have utility in the future for in-text citations to document a particular page number for a quote or other instance where a page number would help.

Here is more information about CIDs for the American Association of Mechanical Engineers and another for EHP Publishing.