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.

What Is a Citation?

When dealing with citations, there are two primary types: forward and backward, or reverse. While the definition may seem simple, forward citations are actually a derived artifact of reverse citations. The type of citation will depend on the point of view.

In essence, all citations will begin as a backward one. To determine a backward citation requires the processing of forms 1449 and 892 in the United States. Foreign jurisdictions will have their own forms. When a patent has been granted, the citations will be listed on the front page of the final published document.

Types of Citations

As mentioned above, there are two primary types of citations your patent may have. A backward citation is a citation of a previously published document that was already available publicly before the new patent application was filed. It is often referred to as prior art.

Backward citations are most beneficial for finding patents that may be related closely and can supplement the classification or keyword-based search. A patent examiner will use backward citations to see the relevance of the previous piece to the current application.

A forward citation will refer to a more recently published piece that has cited the new patent application. These types of citations are considered primarily beneficial in the areas of business intelligence and competition, as they allow the business to identify competitors and other players in that specific technology space.

A business may monitor forward citations on the patent to see new competitors who are using similar technologies, businesses that may be infringing, or businesses that may be perfect for licensing deals. Forward citations were also used as a way to identify which patents were more likely to be purchased. The more forward citations a patent application shows, the higher the interest is.

Reasons for Citing a Patent

There are two principal reasons why a patent might be cited. The first reason is that a backward citation will provide examples of related art. An example of this is an applicant who used citations to inform the examiner that they were aware of a previous piece and crafted their art pieces to avoid duplicating it. In recent years, only about 3 percent of citations were used as a reason for a rejection.

The other — and probably more important — reason is that an examiner may want to cite similar prior art as a reason for patent rejection. The similarities may be great enough that the new piece lacks novelty and is deemed too obvious.

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 following:

  • The European Patent Office (EPO)
  • The Japanese Patent Office (JPO)
  • The World Intellectual Property Organization (WIPO), which issues Patent Collaboration Treaty (PCT) patents

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 innovative 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
  • A 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 to be 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.

Citation Completeness

Unfortunately, a problem commonly found with citations is their lack of completeness. It is estimated that at least half of the patent citations will not be recognized by the person analyzing them, and often the citations are not on the front page of the application where they should be. What's even worse is that with the newer patents, the number of unrecognized citations is even higher.

It is important to remember that both examiners and applicants have the option of citing either granted patents or published applications — though in reality, they cite applications far more than patents that have been granted.

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 that 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, duplicates, 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.

How You Can Use Expanded and Timely Citation Data

There are benefits to using forward data citation. It allows you to have current market data that you would otherwise not see. This can help you:

  • Find out if the competition is developing products that may be similar to yours.
  • File for cited inventions that you may have not officially claimed on your patent through the use of the continuation process.
  • Determine whether an area in the technology sector that holds your interest is going up or phasing out.
  • Evaluate out your activity level when compared to other sectors.

Have this up-to-date and accurate data can also help you take the following actions:

  • Adjust your plans for development to be able to meet your competitor's product head-on and surpass it.
  • Identify problems that you may encounter in regards to licensing or infringement.
  • Determine if the technology you have been protected is losing or has lost its future value, prompting you to not invest in the renewal fees.
  • Find out if you are the most active company in the area where you are planning to introduce services and products that will require protection.
  • Keep an eye out for new competition in your technical space.
  • Determine if your competitor has become aware of your technology.

Resources for Patent Searches

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

  • The USPTO website.
  • The EPO's Espacenet search.
  • The EPO's Common Citation Document website. This lets you search and view documents cited by the five national patent offices (IP5) at once.
  • The WIPO website, which has a search tool for PCT patents.
  • An online tool like PatBase's Citation Explorer. This tool lets users sort and filter citations based on country of origin, publication date, assignee, and=-0examiner relevance codes.

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

  1. Visit the USPTO website. Click on "patents," then "search patents," then "advanced search." From there, you'll input your searches into the query box.
  2. Learn common abbreviations. The USPTO website recognizes the following abbreviations: TTL (title), ABS (abstract), SPEC (description and specifications), and ACLM (claims).
  3. Learn search logic operators. The USPTO recognizes the search terms "and," "and not," and "or."
  4. 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.
  5. 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.
  6. Note the date. As a citation list can grow or change over time, it's important to document the date you searched.
  7. 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 artifical 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

  1. Download and view relevant patents on the USPTO website.You could click to download or use an automated program like uspto1.exe.
  2. 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).
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. Run uspto2.exe on the resulting folder. This will give you the Basefiles, 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.
  9. 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.

Citing Patents and Patent Applications

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.

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.

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 assignees, 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 occurred 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 legal need 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, Menlo Ventures, and Airbnb.