How To Enrich A Prior Art Search Using Citation Analysis?
Patent Search & Analytics Prior Art Search

How To Enrich A Prior Art Search Using Citation Analysis?


A prior art search is conducted to identify relevant published work in a particular domain of technology. There exists a plurality of techniques to conduct a prior art search, among them the keyword and classification based searches are widely used. However, sometimes to find the relevant prior art, these techniques alone do not prove to be adequate and in such a situation, to improve the quality of the prior art search, citation-based searching comes into the picture. It is also known as spider search. The usual searching implementation of citation-based analysis can yield brilliant results.

Before going into depth of the patent citation analysis, we should first understand what is the meaning of patent citation? A patent citation is a document having content related to the content present in the document in which the citation is being made. A patent is generally cited by an applicant or an examiner during the prosecution of patent applications. Patent citations are basically of two-type, viz. backward citations and forward citations.

Backward citations: These are the documents that are publically available before the filing date of a patent application and contain related information. Analyzing backward citation can enhance the prior art searching, as these documents may consist of the closely related prior art, and analyzing backward citation of all the family members of a patent is also very useful as examiners in different jurisdictions cite different prior arts.

Forward citations: These are the documents that are released after the publication of the patent document and contain information related to the patent document. Analyzing forward citations can reveal different patents with technological advancements.

While conducting a prior art search, analysis of both forward citations as well as backward citation of a relevant patent is of highly importance as it can reveal further relevant documents which might not have captured earlier using other searching methods.

Importance of Patent Citation Analysis

There are several reasons why the patent citation analysis is important during the prior art search, some of them are as follow:

Ready to Use Relevant Prior Art

A prior art search can be done using different techniques, among them citation based searching has its own importance as it provides ready to use relevant prior art. The prior art which is listed under patent citations is the prior art that was searched, analyzed and grouped by an examiner, meaning that an examiner has already conducted the prior art search related to the subject patent and has grouped the relevant prior art in the form of a list. Thereby, citation-based searching can efficiently yield relevant prior arts.

Useful in Finding Hidden Prior Arts

Citation based analysis helps in identifying documents that are difficult to find by conducting keyword or classification searches only. While searching for prior art, if only keyword and classification based searches were relied upon, important patent documents of some jurisdictions such as Korea, Taiwan, etc. may remain uncaptured. Citation analysis, if used in addition to the keyword and classification search, can deliver extraordinary results.

Usefulness in Invalidity Searches

Citation analysis can be very helpful in invalidity searches to find relevant prior arts which are being cited in a patent’s family member but not in the patent itself e.g. if there is a European Patent (EP) under investigation for invalidation and there exists a relevant prior art that was not cited by the EPO examiner, resulting in granted claims with a wider scope. And the same relevant prior art was cited during examination by the examiner of EP patent’s US family member, resulting in the narrowed scope of claims in the US. In such a situation, the relevant prior art can be easily identified by using a citation analysis of the complete family of the EP patent.

A Real Scenario In Which We Have Found A Killer Prior Art From Citation Analysis

While doing an invalidation project related to the image capturing apparatus, when we have done a backward citation search we came across a patent which was covering all the elements of the invention except the novel aspect. Then we analyzed the backward as well as forward citation of that reference. We found a patent that was disclosing all the elements of the subject patent including the novel aspect. This is how the citation search helps us to get a promising prior art within a limited time.

Apart from this, citation analysis helps us in improving the technical knowledge regarding a project and provides us a lot of important leads such as relevant keywords, classes, inventors, and the assignee. In addition to the patent literature, it is also possible to analyze the relevant non-patent literature cited in the backward and forward citation. That’s why we consider the citation analysis as the most crucial step for conducting a prior art search.


A good prior art search must leave no stone unturned in the relevant field of technology. All the known methods to identify satisfactory results must be used. It is not possible to enrich the prior art search without performing citation analysis. Citation based analysis not only helps in fostering understanding of the technical domain but also provides related keywords and classifications, making citation analysis an essential part of a good prior art search. It is always advisable to conduct citation searches before using other search strategies to make a strong foundation for a project.

Authored By: Shubham Chaudhary, Research Associate, Operations Team

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