Patent invalidation leads to a 50 percent decrease in patenting by the patent holder, on average, but the impact depends critically on characteristics of the patentee and the competitive environment. The effect is entirely driven by small innovative firms in technology fields where they face many large incumbents. Invalidation of patents held by large firms does not change the intensity of their innovation but shifts the technological direction of their subsequent patenting.Their measure of post-invalidation patenting is the number of applications filed by the patent owner in a 5-year window after the Federal Circuit decision. They also present results suggesting that large firms tend to redirect their research efforts after invalidation of a non-core patent (but not for a core patent), whereas "the loss of a patent leads small firms to reduce innovation across the board, rather than to redirect it." (A "core" patent is one whose two-digit technology field accounts for at least 2/3 of the firm's patenting.)
This is a rich paper with many, many results and nuances and caveats—highly recommended for anyone interested in patent empirics.