Identifying Age, Cohort and Period Effects in Scientific Research Productivity: Discussion and Illustration Using Simulated and Actual Data on French Physicists

The theory of endogenous growth and the geography and growth synthesis both consider that local growth and spatial concentration of economic activities emanate from localised knowledge spillovers (lucas 1988; martin and ottaviano 1999). Since the end of the 1980's, the spatial dimension of knowledge diffusion has been investigated from an empirical point of view, and the existence and role of local spillovers has been generally confirmed (see among others jaffe 1989; audretsch and feldman 1996). The concern that now arises is to unravel the mechanisms underlying and explaining the geographical knowledge spillovers. The aim of this special issue is to present the latest new findings on such questions and to identify some new lines of research for future work. Before presenting the content of this special issue, we very briefly review the main results of the empirical literature on the geography of innovation. We also explain the context of this special issue by pointing out some of the limitations faced by this literature and, by stressing the complex dynamic and network dimensions of the observed processes of production and diffusion of knowledge.