Identifying the Sources of Local Productivity Growth

Using firm-level based TFP indicators (as opposed to employment-based proxies) we estimate the effects of alternative sources of dynamic externalities at the local level. In contrast to previous empirical work, we find that industrial specialization and scale indicators affect TFP growth positively, while neither product variety nor the degree of local competition have any effect. Employment-based regressions yield nearly the opposite results, in line with most of previous empirical work. We argue that such regressions suffer from serious identification problems when interpreted as evidence of dynamic externalities. Our results question the conclusions of most of the existing literature on dynamic agglomeration economies.

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