Pierre-Philippe Combes

The Productivity Advantages of Large Cities: Distinguishing Agglomeration from Firm Selection

Firms are more productive on average in larger cities. Two main explanations have been offered: firm selection (larger cities toughen competition, allowing only the most productive to survive) and agglomeration economies (larger cities promote interactions that increase productivity), possibly reinforced by localised natural advantage. To distinguish between them, we nest a generalised version of a tractable firm selection model and a standard model of agglomeration. Stronger selection in larger cities left-truncates the productivity distribution whereas stronger agglomeration right-shifts and dilates the distribution. Using this prediction, French establishment level data, and a new quantile approach, we show that firm selection cannot explain spatial productivity differences. This result holds across sectors, city size thresholds, establishment samples, and area definitions.

The spatial distribution of economic activities in the European Union

This Paper considers the spatial distribution of economic activities in the European Union. It has three main aims: (i) to describe the data that is available in the EU and give some idea of the rich spatial data sets that are fast becoming available at the national level; (ii) to present descriptive evidence on the location of aggregate activity and particular industries and to consider how these location patterns are changing over time; (iii) to consider the nature of the agglomeration and dispersion forces that determine these patterns and to contrast them to forces acting elsewhere, in particular the US. Our survey suggests that much has been achieved in the wave of empirical work that has occurred in the past decade, but that much work remains to be done.

Product Complexity, Quality of Institutions and the Protrade Effect of Immigrants

The paper assesses the trade-creating impact of foreign-born residents on the international imports and exports of the French regions where they are settled. The protrade effect of immigrants is investigated along two intertwined dimensions: the complexity of traded goods and the quality of institutions in partner countries. The trade-enhancing impact of immigrants is, on average, more salient when they come from a country with weak institutions. However, this positive impact is especially large on the imports of simple products. When we turn to complex goods, for which the information channel conveyed by immigrants is the most valuable, immigration enhances imports regardless of the quality of institutions in the partner country. Regarding exports, immigrants substitute for weak institutions on both simple and complex goods.

Industrial Agglomeration under Cournot Competition

In a two-region model where regional incomes are endogenous and where firms compete a la Cournot, we first show that strategic interactions may induce firms to agglomerate in the initially developed region, if transportation costs are low or economies of scale high: in the region where more firms are established, price and individual market shares effects (intra-regional competition) are counterbalanced by higher global market shares and reduction in imports (inter-regional competition). It is then shown that a regional advantage in costs, productivity or size attracts the location of new firms in this region.

Are academics who publish more also more cited? Individual determinants of publication and citation records

Thanks to a unique individual dataset of French academics in economics, we explain individual publication and citation records by gender and age, co-authorship patterns (average number of authors per article and size of the co-author network) and specialisation choices (percentage of output in each JEL code). The analysis is performed on both EconLit publication scores (adjusted for journal quality) and Google Scholar citation indexes, which allows us to present a broad picture of knowledge diffusion in economics. Citations are largely driven by publication records, which means that these two measures are partly substitutes, but citations are also substantially increased by larger research team size and co-author networks.

Intermodal competition and regional inequalities

Abstract In a model a la Hotelling with discriminatory pricing, we study the impacts of the creation of a new transportation infrastructure that connects two points (as planes or high-speed trains do) and coexists with an old infrastructure that continuously serves space (as roads do). Thus, two transportation modes compete: only road or road plus plane. We characterize the equilibria of a location and price game between two firms. Although airports are symmetrically located, asymmetric equilibria in locations emerge. When the airports are built, relocation of firms induce a decrease of total welfare, if the cost of the transport by plane is not small enough. Regional inequalities appear: in most cases, the welfare of one region decreases when that of the other increases. However consumers’ surplus increases, and firms’ profits decrease. Finally, we study the optimal location and pricing of the new infrastructure.

Common Market with Regulated Firms

We examine the effect of bilateral trade in a concentrated industry under Cournot competition, when firms are regulated by national agencies who care about national social welfare. We allow for differences in costs and market sizes and for asymmetric information between regulatory agencies and regulated firms. A national regulatory policy may or may not be publicly observed by foreign competitors. We show that it is optimal to allow states to subsidize their domestic firms: bilateral trade improves the allocative efficiency and reduces the agency costs of regulation. Strategic trade policy effects that appear when regulatory contracts are public are beneficial to both states and reduce incentive costs as well as allocative inefficiencies. Results extend to the case of segmented markets with export costs when states are allowed to use export subsidies as well as to regulate domestic production. They also extend under perfect information to an arbitrary number of states and regulated firms, to the existence of private importing firms and of a not too large export market.

Climatic information from δ13C in plants by combining statistical and mechanistic approaches

The approach commonly used to assess the potential for climate reconstruction is to use linear regressions to compare the isotopic signal stored in archives to instrumental climatic data sets. A new method is proposed that combines statistical and mechanistic approaches to extract climatic information from δ13C records in organic matter. Both a spatial and a temporal gradient of 13C discrimination in a moss species commonly found in temperate and tropical peat bogs are compared to meteorological records. The relevance of fossil and modem analogues to elucidate palaeoenvironment records are tested. It was found that the magnitude and, in some cases, the direction of the impact of temperature, humidity and CO2 atmospheric concentration on 13C discrimination depend on the calibration set considered. The use of a mechanistic model is shown to help greatly in specifying the joint influence of the climatic variables.

The Production Function for Housing: Evidence from France

We propose a new nonparametric approach to estimate the production function for housing. Our estimation treats output as a latent variable and relies on the firstorder condition for profit maximisation with respect to nonland inputs by competitive house builders. For parcels of a given size, we compute housing by summing across the marginal products of nonland inputs. Differences in nonland inputs are caused by differences in land prices that reflect differences in the demand for housing across locations. We implement our methodology on newlybuilt singlefamily homes in France. We find that the production function for housing is reasonably well, though not perfectly, approximated by a CobbDouglas function and close to constant returns. After correcting for differences in user costs between land and nonland inputs and taking care of some estimation concerns, we estimate an elasticity of housing production with respect to nonland inputs of about 0.80.

Customer Discrimination and Employment Outcomes: Theory and Evidence from the French Labor Market

The paper investigates the link between the overexposure of African immigrants to unemployment in France and their underrepresentation in jobs in contact with customers. We build a two-sector matching model with ethnic sector–specific preferences, economy-wide employer discrimination, and customer discrimination in jobs in contact with customers. The outcomes of the model allow us to build a test of ethnic discrimination in general and customer discrimination in particular. We run the test on French individual data in a cross section of local labor markets (employment areas). Our results show both ethnic and customer discrimination in the French labor market.