We have conducted an empirical study of every reported doctrine ofequivalents decision in both the Federal Circuit and the district courtsduring three periods - one before the Federal Circuit's 2000 Festo opinion,one after that opinion but before the Supreme Court's 2002 opinion, and athird after the Supreme Court's opinion. Two broader findings stand out.First, the multiple changes in the doctrine of equivalents rules over thelast ten years have had surprisingly little effect on the actual outcome ofdoctrine of equivalents cases, and even less effect on the subset of casesdealing directly with prosecution history estoppel. Indeed, to the extentthere is any relationship it is an inverse one - patentees did better underless patent-friendly rules. The attention everyone has paid to Festo aschanging the value of patent rights therefore seems to have been largelywasted from a practical perspective.The second finding is even more significant: the reason the Festo changeshad so little effect seems to be that the doctrine of equivalents wasalready near death by the late 1990s. Even under the permissive doctrine ofequivalents rules in place before 2000, while everyone was focused on thedoctrine of equivalents, equivalents claims usually failed, most often onsummary judgment. That became even more true after 2000, and the SupremeCourt's 2002 decision didn't change the trend. In fact, district courts aremore likely to reject doctrine of equivalents claims today than everbefore.This left us with a bit of a puzzle: what killed the doctrine ofequivalents in the 1990s? We suspected the answer was the growth of claimconstruction Markman hearings after the Supreme Court's 1996 decision inthat case. Once courts were construing claims as a matter of law pre-trial,and finding themselves in a position to resolve virtually all infringementissues on summary judgment, they were naturally inclined to decide thedoctrine of equivalents issues too. And a court that has just rejected aliteral infringement argument - the only courts likely to spend much timethinking about equivalents issues pre-trial - is unlikely to undo the workof claim construction by sending the issue of infringement by equivalentsto the jury. To test this hypothesis, we constructed a fourth dataset,including cases decided in the 1993 to 1995 timeframe. That data bears outour hypothesis. The doctrine of equivalents was alive and well beforeMarkman, but has been in decline ever since.
The Necessity to Restrict the Claim Scope in Applying the Doctrine of Equivalents