From ArsTechnica.

Three Boston University researchers have produced a rigorous empirical estimate of the cost of patent trolling. And the number is breath-taking: patent trolls ("non-practicing entity" is the clinical term) have cost publicly traded defendants $500 billion since 1990. And the problem has become most severe in recent years. In the last four years, the costs have averaged $83 billion per year. The study says this is more than a quarter of US industrial research and development spending during those years.

Two of the study's authors, James Bessen and Mike Meurer, wrote Patent Failure, an empirical study of the patent system that has been widely read and cited since its publication in 2008.