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Bessen & Meurer (2012) estimate that non-practicing entities have accrued $29 million of direct costs to businesses during 2011.[http://www.pcworld.com/article/258395/patent_trolls_cost_tech_companies_29_billion_last_year_study_says.html][http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2091210##] "The authors used a database of 1,630 patent troll lawsuits compiled by Patent Freedom. Because many of the lawsuits had multiple defendants, there was a total of 4,114 plaintiff-defendant pairs. The median defendant over all of these pairs lost $20.4 million in market capitalization, while the mean loss was $122 million."[http://arstechnica.com/tech-policy/2011/09/study-patent-trolls-have-cost-innovators-half-a-trillion-bucks/] The two Boston University faculty members have also published a book, ''Patent Failure: How Judges, Bureaucrats, and Lawyers Put Innovators at Risk'' [http://www.amazon.com/Patent-Failure-Bureaucrats-Lawyers-Innovators/dp/069113491X/arstech-20], where they claim patent trolls "cost publicly traded defendants $500 billion since 1990."[http://arstechnica.com/tech-policy/2011/09/study-patent-trolls-have-cost-innovators-half-a-trillion-bucks/]