What is a patent citation search?

A patent citation search is a patent search of the titles that legally protect inventions from infringement and describe in detail how these inventions look and work based on the references they provide. You can search for patent citations on their own or use a patent citation search to enhance a keyword or classification search.

Understanding Patents

Patents grant inventors the right to exclusively profit from their inventions. They place an inventor's knowledge into a legal realm to protect it against infringement.

The United States Trademark Office (USPTO) grants patents within the United States to original, innovative, functional, and useful patent applications.

Outside the United States, patents are issued by other government bodies including:

The Organization for Economic Cooperation and Development says a patent belongs to a patent family if it's filed at the EPO or JPO and granted by the USPTO. 

The Benefits of Using Patent Data

  • Patents contain highly detailed information about inventions. This information, including details about technological areas, inventors, and assignees, reveals a lot about innovation practices and evolution around the world.
  • There are a great number of patents. More than 150,000 patents are published every year. This means any patent database holds a massive amount of research data. 
  • Patents have a rich history. Inventors have obtained patents in the United States since the late 18th century. The current numbering and reporting system dates back to the 1870s. That means there is more than a century worth of information in most patent database systems. 
  • Patent data is offered on a voluntary basis. This contrasts with other types of economic information, which is collected without consent.

Citations in Patents

A patent citation is any document cited by a patent applicant, a third-party, or a patent office examiner because it's relevant to a patent application. A patent can cite any public document, such as:

  • An existing patent
  • A journal article
  • An website or online article
  • A seminar abstract or speech
  • Oral information

Citations give context to the patent and the technology and innovation behind it. Patent authors and examiners both add citations to patents. Ultimately patent examiners decide which citations are relevant and which are not. After a patent's publication, the citation list can map an invention's development. Citations in patents reveal links between inventions, inventors, scientists, locations, and businesses which can be fascinating to explore. 

Patent citations can include backward citations or references (cited works) or forward citations or references (citing works).

  • Backward citations: earlier published documents available before a patent application was filed. They are sometimes called prior art. Searching for backward citations can help you find closely related patents and literature. Reviewing the backward citations of all patent family members can be helpful since different patent examiners typically cite different backward citations.
  • Forward citations: more recent documents released after a patent's publication. If patents are republished, they may cite relevant documents published after their original publication. These forward citations will not appear on the paper patent, as these are not amended, but they may appear on republished electronic versions. Searching for forward citations can reveal the latest information and new competitors in a particular field. More recent published patents will have fewer forward citations than older patents.

The quality of patents varies significantly. Searching using citations can be a good way for inventors to find informative patents relevant to their own inventions. Studies show patents that are commonly cited have more economic worth than those that are rarely cited. Patents that are often cited are also thought to have greater technological significance. 

In fact, forward citations are considered by many the most important factor for ranking the value of patents, especially those in the tech field. The age of the patent from its priority date, the independent claim count, Claim 1 word count, and family size and international filings are also important.

Problems With Patent Citation Searches

Since patent citation is viewed as very valuable, looking at patent citation is the most popular method of objectively analyzing patents. However, this doesn't mean patent citation analysis is always valuable. You should avoid making assumptions about the creation of patent citations. In many cases, patent citations don't reveal anything about a relationship between two patents.  

While examiners are trained to find the best prior art, they can overlook patents which are technologically significant and relevant. This means that worthy patents aren't always cited.

Information shared between inventors and companies based on citations can't be shown to exist where:

  • The examiner finds patents for citing
  • A professional searcher finds patents for citing
  • The inventor or representing attorney finds patents during patent preparation

Patent citations are also corrected if they're incorrect, duplicate, or not citations at all.

Inventors may be inspired by a range of things that can't be cited such as television programs and their own experiences. They will cite patents in their application because they have to, not because the patents really played a key part in their invention's development.

We don't know which patent citations are affected by these factors and which are solid citations. That's why analyzing patent citations is so problematic.

Resources for Patent Searches

You can conduct patent citation searches using a number of online intellectual property agency databases.

The Member States page of the World Intellectual Property Organization also lists further intellectual property agencies from around the globe. 

Conducting a USPTO Patent Classification Search

  • Visit the USPTO website. Click on patents, then search patents, then advanced search. You'll input your searches into the query box.
  • Learn common abbreviations. The USPTO website recognizes the abbreviations:
    • TTL: title
    • ABS: abstract
    • SPEC: description and specifications
    • ACLM: claims
  • Learn search logic operators. The USPTO recognizes the search terms and, and not, and or.
  • Conduct a basic keyword search. To search for all patents with the word computer in their title, type TTL/computer into the query box. You could refine the search to find all touchscreen computers by typing: TTL/"computer interface" and spec/touch. 
  • Search for backward and forward citations. Most patent searching databases have backward and forward citation search functions. Using both provides a w2complete picture of an invention's development and its place in its field. 
  • Note the date. As a citation list can grow or change over time, it's important to document the date you searched. 
  • Use the help section. The USPTO help page provides useful assistance, especially the "tips on field searching" section.

Working With Search Results Using the Fixed-Effects Approach

The fixed-effects approach involves scaling citations by the average number of citations for a patent group to which the target patent belongs.

  • Count the number of times a patent was cited by others.
  • Count the average number of times other patents in the same group are cited.

For example, consider Patent A. It is cited by 11 other patents. Other patents in Patent A's group receive 10 citations, on average.

Patent A is as valuable as Patent B, which received 33 citations and belongs to a group with an average of 30 citations. It is not as valuable as Patent C, which has 3 citations and belongs to a group with an average of 1 citation.

This approach is a good one because analysists don't need to make assumptions about why the groups have different citation numbers. However, because there are no assumptions made, the approach doesn't differentiate between real and artifactual variations.

Working With Search Results Using the Quasi-Structural Approach

The quasi-structural approach uses econometric estimation to distinguish the different effects on citation rates. It doesn't simply accept that different groups and patents have different citation numbers and rates. It looks deeper and attempts to discover why.

This approach has the advantage of delivering more in-depth analysis. However, the assumptions people make using the quasi-structural approach may be incorrect. 

Analyzing Patent Search Results With Loet Leydesdorff Programs

  • Download and view relevant patents on the USPTO website. You could click to download or use an automated program like uspto1.exe.
  • Analyze patents using uspto2.exe. This program will analyze the html patent files, searching for keywords like assignee and title. It will then convert them into dBase files viewable in Access (and Excel if you prefer).  
  • Create an Access database for viewing new files. Create a blank database and import the .DBF files into it. You'll see the files under the tables section. Clicking on each one opens the related table. 
  • Link related tables. Click the relationship button in the main window, then highlight each relevant table and click add. Create a unique identifier for each relationship group.
  • Remove duplicates. Patents with multiple classes will show more than once. Right-click on the 1 in the CLASSNR field and exclude the other results. Go to the query work window, right-click the gray area, then properties, and set the unique values to "yes." Then re-click the red exclamation point. 
  • Create a query for patents you want to reference. Click the query button in the design window, then highlight the tables you want and click add. Make sure you add the PATNR column as this has the patent numbers. Click and drag relevant sections from each section, then click the red exclamation point to show the results. 
  • Use Patref.exe programs. Copy the list of patent numbers into a text document (list2) and place it in the same folder as the patref0.exe program. Run the program and note how many patents you want processed. Use Patref1.exe to extract another list from these files, which you can use in Patref2.exe. Patref2 downloads patents citing the patents from list2 from the USPTO database. Run uspto2.exe on the resulting folder to get the dBasefiles, TI, ASS, INV for the citing patents. You can open these on Access as before. Create a new database called something like Citing and change the names of the fields to avoid confusing them.
  • Match the original patents and the citing patents. You could do this in one database, but it's less confusing if you open the patents in separate databases. Import the .DBF files as before. Open a new relationship window and add the files you need, including the relevant tables. Link them using the Citing table and compare your results.

Frequently Asked Questions

  • What should I look for in a ranking system?

Ranking systems can be an excellent way to efficiently sort through patents to find documents of value. Any ranking system you choose should be:

  • Fully transparent. You should know how the system calculates its results.
  • Clear and data based. Each factor should be based in data, rather than assumptions. It should also be clearly explainable.
  • ​​How do I cite patents and patent applications in my own papers?

Citations should be brief and follow a set format, without sentences. The correct citation method depends on the style guide you follow. Citations often list the names of two types of authors: inventors and assignees. An assignee is the person or group that legally owns the patent. List names in the order they appear on the patent, with the surname first.

Instead of listing a publisher and its location, as you would a book, citations typically list the name of the country that granted the patent and its patent number. Countries receive their adjectival form, except for United States and United Kingdom. Patents may be issued by regional offices on a country's behalf. Patents with numbers beginning with EP were issued by the European Patent Office. Numbers beginning with WO come from the World Intellectual Property Organization, cited as "world patent."

The word application is always used to show a pending patent's status.

  • American Chemical Society (ACS) Style (3rd edition, 2006, page 310)
    • Format: Inventor name 1; Inventor name 2; etc. Patent title. Patent number, Issue date.
    • Example: Costa, M.E.; Nguyen, H.P. Camera Housing Ball Mount. U.S. Patent No. D777,239, January 24, 2017.
  • American Psychological Association (APA) Style (6th edition, 2009, page 224)
    • Format: Inventor name 1, Inventor name 2; etc. (Year Issued). Patent number. Source.
    • Example: Kim, E.J., Van Komen, C. (2017) U.S. Patent No. 9,554,449. Washington, DC: U.S. Patent and Trademark Office.
    • Within text, you only need to cite the patent number and year issued e.g. U.S. Patent No. 9,554,449 (2017). 
  • Chicago Manual of Style (16th edition, 2010, section 14.230)
    • Format: Inventor name 1, Inventor name 2; etc. Patent title. Patent number, and date of filing and issue.
    • Example: Ananda, S., Cross, J.M. Planter bag. U.S. Patent D777,056, filed June 29, 2015, and issued January 24, 2017.
  • Council of Science Editors (CSE) Style (8th edition, 2014,section
    • Name-Date Format: Name(s), inventor(s); Name, assignee. Date. Patent title. Country issuing the patent country code patent number. Extent.
    • Example: Kogure, K, Toduka, M, inventors; Hitachi Chemical Company Ltd, assignee. 2017 Jan 24. Lead-acid battery. United States patent US 9,553,335.
    • Citation-Sequence and Citation-Name Format: Name(s), inventor(s); patent holder, assignee. Patent title. Country issuing the patent country code patent number. Publication date. Extent.
    • Example: Kogure, K, Toduka, M, inventors; Hitachi Chemical Company Ltd, assignee. Lead-acid battery. United States patent US 9,553,335. 2017 Jan 24.
  • Modern Language Association (MLA) Style (No style given. Format based on other citation examples)
    • Format: Inventor name 1; Inventor name 2; etc. "Patent title." Patent number. Date.
    • Example: McMahon, Liam. "Guitar Hurling Stick." U.S. Patent D777,244. 24 January 2017.
  • International Organization for Standardization (ISO) Style (ISO Standard 690:2010(E), Information & Documentation - Guidelines for Bibliographic References and Citations to Information Resources,section 15.9)
    • Format: Inventor name 1, Inventor name 2; etc. Patent title, Country name or code and official designation of series within patent resource. Patent serial number is adequate numeration.
    • Example: Phipps, Emerson S., Phipps, Charles E. Protective Helmet, U.S. Patent 9,549,582. 
    • Non-U.S. publications may use this style
  • Institute of Electrical and Electronics Engineers (IEEE) Style
    • Format: Inventor name 1, Inventor name 2, etc. "Patent title." Patent number, issue date.
    • Example: Y. Shigeno, "Music Synthesizer." U.S. Patent 9,542,923, issued January 10, 2017.
  • Bluebook Style
    • Format: Patent number (issue date).
    • Example: U.S. Patent No. 9,530,394 (issued Dec. 27, 2016).
  • American Medical Association (AMA) Style
    • Format: Name 1, Name 2, etc. inventor; Name, assignee. Patent number. Issue date.
    • Example, Durand, J, Durand, L, Grenien, M, inventor; Theratechnologies Inc., assignee. U.S. patent 5,602,924. February 11, 1997. 
  • National Library of Medicine (NLM) Style
    • Format: Name 1, Name 2, etc. inventor; Name, assignee. (Author affiliation) (optional), Patent title. [Type of medium] (only if patent published in microform). Country Patent document type (simply type patent for U.S. other countries may list different types) ISO country code Patent number. Issue date. Pagination p (optional). Physical description (optional). Int. Cl. International Classification Code (optional) ISO Country Classification Code Cl. (optional) Appl. No. Application number (optional); Application filing date (optional). Language (if not English).
    • Example: Foster Jr., L.H, inventor (Zephyr Cove, NV). Gunther Pacific Limited of Hong Kong, assignee (Central, HK), Weight loss device and method. United States patent U.S. 4,485,805. 1984 Dec 4. Int. Cl. A61F 5/00 (20060101); A61B 19/00 (20060101); A61B 017/00 (). Appl. No. 06/411,053; 1982 Aug 24.
  • I'm still not confident citing author (inventor) names using the NLM Style. Can you give me any more tips?
    • Start with inventors' names. Every citation should begin with the inventors' names listed in the order they appear on the patent.
    • List surname first, then first (and middle, if available) initial. Surnames should be capitalized and spaced as on the patent e.g. de Burgh or DeBurgh. No more than two initials should follow each surname.
    • List all inventors. It doesn't matter how many inventors there are; they all deserve a place on your citation.
    • Separate inventor's names with a comma and space.
    • Put a comma and the word inventor or inventors after the last inventor name.
    • End with a semicolon and space.
  • I'm still not sure how to cite author (assignee) names using the NLM Style. Can you give me any more tips?
    • List the assignees' name after the inventor(s)'s names. Assignee are sometimes called proprietors or applicants.
    • Write the assignee name as listed on the patent's title page. Include all abbreviations and punctuation marks as written.
    • List surname first, then first (and middle, if available) initial. Surnames should be capitalized and spaced as on the patent e.g. de Burgh or DeBurgh. No more than two initials should follow each surname.  
    • List all assignee, regardless of how many there are.
    • Separate assignee names with a comma and space.
    • Put a comma and the word assignee after the last assignee name. Assignee is used for one or many assignee.
    • End with a period.
  • I want to purchase a license for someone else's patent. How old should it be?

You'll probably want a patent that's currently established in its industry, yet not so old that the investment isn't worthwhile. Patents that are 8 to 12 years from priority are usually the most valuable for licensing deals. If you want to buy the patent for a potential dispute that hasn't occured yet, the patent should expire in no less than 5 years. There's a wealth of further online information about the timing of litigation and life of patents. 

If you need help with a patent citation search, you can post your question or concern on UpCounsel's marketplace. UpCounsel accepts only the top 5 percent of lawyers to its site. Lawyers on UpCounsel come from law schools such as Harvard Law and Yale Law and average 14 years of legal experience, including work with or on behalf of companies like Google, Stripe, and Twilio.