Guest Post by Prof. Yelderman: How Do District Courts Cite Prior Art?

Stephen Yelderman is a Professor of Law at the University of Notre Dame Law School.

Not all prior art is created equal. The ease of finding what’s been done before can vary dramatically—from a prior U.S. patent cited by hundreds of applicants, to the dusty doctoral thesis sitting on the shelf of a foreign library. So one might wonder: when district courts invalidate patents on prior art grounds, do they typically rely on prior art that the inventor, or the USPTO, or even a reasonably diligent searcher could plausibly have found? Or do courts regularly invalidate patents on the basis of art that only the most determined litigant could have possibly uncovered?

For the last year or so, I have been working with a team of research assistants to attempt to answer these and other questions. Drawing directly from district court dockets, we collected every decision invalidating a patent claim over a six-and-half-year period. We then coded these on a claim-by-claim, reference-by-reference basis to learn how district courts rely on prior art. Over the next several weeks, I’ll be highlighting some of the more interesting things we’ve uncovered. In this post, I’ll start by sharing some of our top-level findings and briefly explaining our collection methodology. (If you’d like to see our full results right away, a draft of the paper is available for download here.)

First, some may be surprised to learn that district court invalidation appears to be evenly split between anticipation and obviousness. This is true whether one measures by patents or claims:

Over our study period, the number of claims invalidated for anticipation (1,636) almost exactly equaled the number of claims invalidated for obviousness (1,620). As the chart above shows, while there was some up and down from year to year, the ratio held very close to 1 throughout our study period.

However, the similarities end there. In terms of the prior art relied upon to invalidate claims, anticipation and obviousness are two very different animals:

The black columns indicate the percentage of anticipation invalidations citing each category of prior art. As you can see, district court findings of anticipation rely predominantly on activity prior art (defined to include prior uses, sales, and invention by another—old § 102g).  After that, in descending order of frequency, come U.S. patents, printed publications, and foreign patents.

Obviousness invalidations are a bit harder to summarize concisely, since they can be based on multiple references. The hashed columns indicate the percentage of obviousness invalidations citing any art in that category; the gray columns indicate the percentage of obviousness invalidations citing art only in that category. The headline here is that U.S. patents are by far the most commonly cited category of prior art for obviousness: nearly two thirds of obviousness invalidations cite at least one U.S. patent. But less than one third of obviousness invalidations cite only U.S. patents. A similar theme bears out across the rest of the chart. When courts combine multiple references to find a claim obvious, they often do so by combining art across categories—a U.S. patent combined with a prior sale, for example, or a foreign patent combined with a printed publication.

Each of these top-level categories will be explored in more detail in subsequent posts. I’ll close this one with a bit of background about our collection methodology. For purposes of this study, our focus was limited to claim invalidity as found by district courts. Therefore, our data does not capture every distinct argument the defendant made for invalidity, or judicial findings that a claim was “not invalid.” It also does not reflect the ways these decisions may have been modified on appeal. We believe our data does capture every district court determination that a claim was invalid, whether in a published opinion, unpublished document, or jury verdict. In a few cases, these documents did not clearly specify on their face which references supported the conclusion of invalidity. When this occurred, we consulted other documents on the docket (such as post-trial briefing) to identify the prior art supporting the court’s conclusions. When we could not find a conclusive answer, we coded the prior art as “unknown” (the final category in the chart above). Additional details about how we collected and coded these documents can be found in Part II of the paper.

Finally, when interpreting all of this data, one should keep in mind that this is a study of how district courts cite prior art, not a study of patent quality overall. A tiny fraction of issued patents are ever litigated, and only a tiny fraction of those are litigated to a determination of validity. Moreover, the incentives to litigate or settle a patent dispute could very well turn on the nature of the prior art in a case, so the possibility of selection effects is real. Therefore, this data should only be used to answer questions about why patents are invalidated in district court, not why patents might be invalid in general.

21 thoughts on “Guest Post by Prof. Yelderman: How Do District Courts Cite Prior Art?

    1. 5.1

      “It’s a disgrace when every case gets filed in the 9th Circuit,” Trump said as part of a lengthy criticism of the court. “That’s not law. Every case in the 9th Circuit we get beaten and then we end up having to go to the Supreme Court like the travel ban and we won. Every case, no matter where it is, they file is practically, for all intents and purposes, they file it in what’s called the 9th Circuit. This was an Obama judge. I’ll tell you what, it’s not going to happen like this anymore.”

      Perznit D00shb@g sounds like he’s been sm0kin’ Night Wiper’s meth.

  1. 4

    Has anyone a idea why the “Obviousness (all) – US patent” is so high? I would have thought that in these cases, the defendants would file an IPR for a fraction of the cost of a full trial.

  2. 3

    3,256 claim total…?


    Not patents, but claims.

    And that’s cumulative over a 6+ year period?

    So, about 550 claims a year.

    If we normalize the numbers against the TOTAL number of possible claims — all active patents plus naturally expired patents for up to six years old multiplied by some reasonable estimate of claims per patent — in order to arrive at a relative indicator of just how “bad” it is that all these “nasty” patents are out there driving that “patents are bad” mantra.

    That normalized number would be shockingly low and would be an interesting “check” against that drumbeat of “bad patents” and “Tr011s;” not to mention providing a relative “noise” estimate even if every court case is captured.

    1. 3.2

      Fun and games with “statistics” Anon? Nobody cares about invalidating the huge majority of all patents that no one is ever being threatened by. In contrast to the few hundred patents per year that the patent owners think are so valuable that they are worth fighting all the way through a million dollar plus trial even after all defendant arguments. A less typical little abnormal set of patents to draw validity conclusions as to all patents from would be hard to find. Much less to compare them to the total number of patents rather than the small number of patents that go to trial and get an invalidity each year. Especially since the majority of District Court decisions for defendants are on non-infringement.

      1. 3.2.1

        Fun and games?

        Not at all – just a little perspective added if one normalizes.

        There has been SO MUCH emphasis on “bad patents,” that the perspective has been completely lost.

        You say “nobody cares” about all those others….

        That – in and of itself – is part of the problem.

    2. 3.3

      “anon” you should actually be normalizing against all the claims that weren’t filed because some of us advise our clients not to bother, or because clients don’t want to pay the fees for the claims.

      I estimate that is approximately 1 or 2 billion additional claims to add to the denominator.

      The bottom line either way is that there clearly is not enough patent litigation. Until every American has been sued for patent infringement — preferably for programming a computer or thinking about a correlation — every American won’t understand what True Freedom (TM) feels like. And if every American doesn’t understand True Freedom (TM), then how can we expect democracy to function.

      Perhaps a good start would be to allow only people who own patents or who have been sued for patent infringement to vote. Only then can sanity and greatness be restored to our increasingly Amishized country.

      1. 3.3.1

        claims not filed…?

        Um, no.

        I’m merely pointing out granted claims (and quantity thereof) that has a meaningful relation to the “scourge” of “bad patents.”

      2. 3.3.2

        The bottom line either way is that there clearly is not enough patent litigation.

        Nice strawman.

        Maybe you should pay attention to the points I present instead of your (usual) dissembling. My point has nothing to do with “more litigation.”

        As to “programming a computer,” why are you SO anti-patent when it comes to innovation MOST accessible to the non-1-percenters? Do you not understand innovation? (for example, maybe you should read some Schumpeter on innovation)

        As to “true freedom” and your attempted dissembling with “patriotic” themes, this is just more dissembling nonsense from you, and has zero to do with any of the points that I put to you. But it does sound in your usual Trump-like self (and your penchant for Accuse Others).

        As to “ allow only people who own patents or who have been sued for patent infringement to vote,” you double down on your inanity, with yet another strawman AND you miss (and miss badly) the point that I DID present that highlights how overblown this whole “”but I got sued on a bad patent” mantra is.

        Pay attention son.
        Start actually replying to the points I present (and stop being your usual arse).


          you miss (and miss badly) the point that I DID present that highlights how overblown this whole “”but I got sued on a bad patent” mantra is

          Ray Niro just called. He wants you to know that he’s dead and you don’t need to s_ck his d_ck anymore.

    3. 3.4

      that drumbeat of “bad patents”

      McRo! Enfish! McRo! Enfish! McRo! Enfish!

      I guess there is a certain beat if you emphasize the first syllables.

    4. 3.5

      If you actually care about this (and not just debating strawmen), then pick 100 (or 10) recently issued patents at random and file the best IPRs or ex parte reexams you can. Let us know the results. Do it across several art units and compare.

      1. 3.5.1

        Good idea. But who is going to spend the roughly $150K each for 10-100 really thorough prior art searches and IPR petitions on randomly picked patents? Hint, Not a law school prof.

      2. 3.5.2


        Who are you responding to? I ask because your reply here has nothing to do with my suggestions at post 3, and I was certainly not “debating strawmen” as you seem to indicate.

  3. 2

    Delighted to see this study of District Court invalidity decisions – finding 1,636 claims invalidated for anticipation, almost equal to the number of claims invalidated for obviousness (1,620), over a six and a half year sample period.*
    I was not surprised to see the anticipations were found to predominantly be from prior uses, on-sales, and prior inventions. None of those defenses were available in any PTO proceeding, other than a relatively insignificant number of interferences.
    But the unobviousness determinations raise several questions that will be of even more practical interest to practitioners. How many were due to reexaminations, IPRs or ITC proceedings? How many were based on the contents of publications rather than just prior patents? Especially, more obscure publications. How many were based on previously-prosecution-cited patents or publications that were rendered much more effective by expert testimony in the DC?
    How does the study deal with the fact that roughly 95% of all patent suits are settled before trial, with no way to know how much the defendant’s uncovered prior art influenced that settlement? We know that some portion of those settlements were so triggered.

    *some patent blog commentators seem to think only IPRs invalidate many issued patent claims.

    1. 2.1

      BTW, if we are only looking at [sustained?] patent trial verdicts, the high percentage of claims invalidated for anticipation, almost equal to the number of claims invalidated for obviousness* seems largely explainable by juries being far more easily convinced by good defense counsel presentations of prior uses, sales, or inventions by others. That is “conventional wisdom” among many patent trial lawyers.
      *[very different from rejections of PTO application claims or IPR claims, where 103 rejections are far more common than 102.]
      Also, if a defendant has a good fully anticipatory [102] patent or publication why would they not be almost obligated to file an IPR in the best interests of their client?

  4. 1

    this data should only be used to answer questions about why patents are invalidated in district court, not why patents might be invalid in general.

    Maybe a better word than “why” would be “how”.

    Nice article, in any case, and I look forward to reading the rest of the series.

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