In most patent lawsuits, the defendant invented independently [pdf]
law.berkeley.edu
law.berkeley.edu
So unless we know what percentage of people were stopped from copying someone else's work without the need for a lawsuit, this study alone doesn't tell us very much about the social costs and benefits of patents by itself. I tend to believe that our patent system is too strong and I might very well mention it in discussions with proper caveats, but we need more research.
It also does say something about the "benefits" of the patent system, though less strongly: clearly if the vast majority of people being sued in particular industries are independently inventing things, that means that the knowledge transfer benefits of patents in those industries is likely over-stated by pro-patent lobbies.
In other words, in the race to invent and patent, first place gets a big prize, second place is the first loser.
One could argue that perhaps that low incidence is simply due to people not bothering to allege copying since it isn't relevant to if infringement occurred. The authors suppose that that's unlikely, since copying is highly relevant to the question of whether or not willful infringement occurs, and their limited evidence suggests that findings of copying do in fact tend to lead to findings of willful infringement. To test that hypothesis, they gathered up an additional 102 cases where evidence of copying was found and found that in nearly 2/3 of them copying was alleged by the plaintiff. (pp. 28-29 in the pdf). That would seem to be fairly strong evidence that if a plaintiff has actual evidence of copying they're highly likely to allege copying somewhere in their complaint.
Thus, it's a reasonable conclusion that since only 10% overall of patent litigations involve even allegations of copying (and far fewer for anything outside of pharma or chemical patents), that most cases where there's actual evidence of copying result in such allegations, and that allegations themselves are merely an upper bound on actual copying (since the allegations may well be untrue), that there's actually not much copying going on, which means that most of the inventions being sued over were produced independently rather than through any kind of "copying" or "theft."