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Patent citations are similar to citations referenced in scholarly research bibliographies or works cited. The major difference being that patents are typically only referenced by name(s) of the patent owner (inventor, assignee, or corporate patentee), the patent number, date, and often, the patent title is included too. Unlike references cited in journals, cited patents are not always chosen by an author/inventor. References cited in patents are furnished by a patent examiner at the issuing patent office. It is highly recommended to refer to specific citation style guides (e.g. MLA, APA, etc.) for detailed patent reference formatting in reports. For instance, the American Chemical Society* recommends the following format:
Patent Owner 1; Patent Owner 2; etc. Title of Patent. Patent Number, Date, e.g.: Darrow, Charles B. Board Game Apparatus. U.S. Patent 2,026.082, December 31, 1935.
Patent citations include backward(cited work) or forward (citing work) references. For example:
Patent A is granted in 2005 for a gizmo, while Patent B is granted in 2015 for a gizmo with new patentable improvements. Patent B lists Patent A as a cited work, while Patent A could be re-published in an electronic database citing Patent B. Patent A is a backward citation of Patent B, while Patent B is a forward citation of Patent A.
Forward citing works cannot appear on the originally issued paper format of a patent since they are not amended, though forward citing works can appear on the patent record published in electronic databases. As a result, most patent searching databases offer both backward and forward citation searching. It is important to note that the number of referenced citations of a patent increases with time. Consequently, it is important to also record the date(s) the patent was accessed within the cited reference(s). For more about prior art patent citations, see Retrieval and Comparison of Prior Art Citations by Lutz Mailänder of WIPO (World International Property Organization).
Patent Citation Databases
One of the more comprehensive free access sites to locate an entire international family of patents is the European Patent Office (EPO) patent searching database https://worldwide.espacenet.com/. A patent family is the same invention disclosed by a common inventor(s) and patented in more than one country.** The EPO database provides cited (backward) and citing (forward) patent family documents. The EPO has recently introduced the Common Citation Document (CCD) and its website http://www.epo.org/searching/free/citation.html. CCD site is unique in that is allows users to search for and view all documents cited by the five national patent offices, known as the IP5, https://www.fiveipoffices.org/index at once. Currently, the five offices include sites in Europe, Japan, Korea, China, and the United States. The CCD combines the patents cited by all contributing patent offices for a patent family member of an application, thus facilitating the search results for the same invention produced by several patent offices via a single view.
*Source: ACS Style Guide: Effective Communication of Scientific Information, Editor(s): Anne M. Coghill, Lorrin R. Garson, Publication Date (Print): June 01, 2006, Copyright © 2006 American Chemical Society.
**Source: U.S. Patent & Trademark Office, Glossary, Patent Family definition, http://www.uspto.gov/learning-and-resources/glossary (accessed April 08, 2015).