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Improving your patent searching using citation analysis

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"What's in a name? That which we call a rose

 By any other name would smell as sweet"

Wrote William Shakespeare in one of his most well known play's "Romeo and Juliet" many centuries ago. But does the same apply to patent searching?

Names, and particularly technical words are particularly important when searching patents. For this reason a whole field had developed to improve searching using keywords, sometimes referred to as 'semantic searching". Keyword based searching does have a couple of important natural limitations to deal with though:

  • Different patent applicants (or their attorneys) use different technical words for the same concept. For example, if we take the easy to understand area of patents for cardboard boxes, different applicants can use the technical words 'box', 'carton', 'container', 'package' and 'carrier' all to describe the same concept.
  • A technical word or combination of technical words can include a wide variety of inventions. Returning to the world of cardboard boxes, there are thousands of different patents that cover different variations of cardboard boxes. However a patent attorney when drafting such patents is limited in the range of technical words they can use to distinguish one invention from another - for example 'top', base', 'side', 'flap' etc (and in fact every technical area has a limited set of technical words that are combined in different ways to describe different inventions). So a given patent search using a given combination of technical words can bring up a wide range of inventions.


Combining a keyword search with a International Patent Classification (IPC) or US patent classification codes can improve matters, but again limitations appear:

  • A given IPC patent code can cover a range of a inventions within a given technical area.
  • IPC codes can be imperfectly assigned, particularly when codes are translated from one classification system to another, for example from USPTO patent codes to IPC codes, or vice-versa.

But of course, we all know this. Anybody who has ever reviewed a list of patent search results would have waded through a whole set of mostly irrelevant patents before finding the patents they were looking for. Patent examiners can spend hours seaching for relevant patents, even using some very sophisticated patent searching tools.

This is an alternative though, and more and more people are using citation analysis to augment their keyword searches. During patent examination either patent applicants or examiner identiify similar patents, and the resulting patent citations are publicly available. The advantage of citation analysis is that links can be made between patents based on the inherant subject of the patents, i.e independently of the technical word used. A patent examiner instinctively knows that a 'box' is a 'carton' is a 'container', to give but one example. Similarly, patent citations are generally made to patents disclosing similar inventions, but not to every patent in the technical field. So inherently, using patent citations to identify similar inventions has the potential to bring a lot of precision to the patent searching task.   

However, even citation searching has its limitations:

  • Some individual patents can have hundreds of patent citations, creating an additional large group of patents to wade through in order to find the patents you are looking for.
  • Sometimes patent examiners, particularly US patent examiners, can identify an invention which is similar to the patent being examined, but which might be a missing a key feature (hence the patent being examined is novel over the prior art patent). The examinar then identifies a second patent disclosing the missing feature from what can be a different technical field, and then states words to the effect 'if you combine these two otherwise unrelated patents, the invention being claimed is not inventive". Besides being frustrating to patent applicants, this type of prior art analysis also creates what can be a citation link to a very different invention, in what can be a different technical field.    


Network Patent Analysis (NPA) uses a different approach to analysing citation connection. It looks for supporting evidence (similar citation links) to weight the importance of a given citation link. Weighting of citation links is then used to help identify clusters of patents of very similar subject matter, with the relative importance of these patents emphasised. Weakly connected patents (due to being in another subject matter area) are ignored. Results are presented in a visually insightful manner, as shown in the figure below. The visual cluster can even be used to suggest similar patents that are not directly citationally connected to the patent in question.

Figure: Example of cluster analysis from an upcoming NPA white paper on Alzheimer's patents. Another examples of cluster analyis, applied to smartphone patents, is found here.



This relieves the patent analyst, attorney or lawyer of the burden of having to wade through what can be hundreds or thousands of unrelated or only loosely patents. Instead they can concentrate on the most similar and most influential patents in the field, saving time and money, and reducing the risk, of missing key patents.  Or in other words, NPA brings a new level of both:

  • precision (focusing in particular inventions) and
  • generality (by bringing in inventions that can have different keywords or patent codes, and allowing objective analysis of tens of thousands of patents).

into patent searching.

Or in other words, we believe that the words of Shakespeare can be applied to patents - a patent by another (technical) name can smell as sweet... 


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Mike first developed an interest in patent data when working as a research scientist, and deepened this interest when working as an IP manager which led to his role at Griffith Hack. Mike has published in the areas of chemical engineering, patent management, the value of patents and the use of patent data in in a wide range of publications and forums, including the international journals Les Nouvelles, and Managing Intellectual Property.