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Abstract

Using large-scale data on opposition to patents at the European Patent Office (EPO), we investigate the causal effect of a patent’s invalidation on follow-on inventions. We introduce a new instrumental variable exploiting the participation or absence of the patent examiner in the opposition proceeding. According to our baseline model, patent invalidation leads to a highly significant and sizable increase of forward citations. While this is in line with previous studies, disentangling the effect leads us to results that stand in stark contrast to some of the literature. We find that the effects are most pronounced for patents in discrete technology areas, for areas where patent thickets are absent and for patents which are not protected by ""patent fences"". Moreover, the effect is particularly strong for relatively small patent holders facing comparatively small follow-on innovators.