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α: calibrated so average coauthorship-adjusted count equals average raw count
This paper studies the social desirability of agglomeration, and the efficiency arguments for policy intervention in a simple, analytically tractable new economic geography model. The location pattern emerging as market equilibrium is 'bubble-shaped', i.e. it features dispersion both at high and low trade costs and stable equilibria with partial and full agglomeration for intermediate levels of trade costs. We show that the market equilibrium is characterized by over-agglomeration for high trade costs and under-agglomeration for low trade costs, and we work out analytically that a net pecuniary externality is the underlying cause of this market failure. One particularly noteworthy result is that the net pecuniary externality is positive at high levels of trade freeness. However, there is no market under-agglomeration unless this positive net pecuniary externality interacts with an additional congestion force originating in the (per se efficient) competitive housing market.