Empirical studies of the diffusion of scientific and technological knowledge: some methodological considerations

I review recent methodological developments that have great relevance for the study of the effect of intellectual property rights (IPRs) on the diffusion of scientific and technological knowledge across time, space, field, and institutional boundaries. In particular, I emphasize two aspects of study design for empirical work that have become increasingly (but not universally) recognized: (i) the need to identify "useful" regime shifts; and (ii) the selection of valid papers or patents to serve as controls.