Peter Zura writes at his two-seventy-one patent blog:
Over the past 5 years or so, there has been an increased focus on the empirical outcome of patent litigation, primarily because the number of such lawsuits have increased noticeably. Jay Kesan & Gwendolyn Ball from the University of Illinois have published a recent study titled "How Are Patent Cases Resolved? An Empirical Examination of the Adjudication and Settlement of Patent Disputes." The study builds on previous findings that detail many of the pathologies of the litigation process.
Using the courts to invalidate patents at trial doesn't appear to be an effective policy. Despite the greater ability of the court system to review all evidence pertaining to the validity of patents, less than 2.5% of litigated patents appear to be "weeded out" every year in the courts. Combined with reexamination requests, and average of 300 patents a year were invalidated in the mid-90's (as compared to the roughly 300,000 patents that were granted each year).
Read the full post here.