An Idea Flows Theory of Entry, Trade and Growth--论文代写范文精选

动态选择效应是一种新的收益来源，校准模型意味着动态选择大约三倍的收益，与静态的贸易是一种异构关系。贸易如何影响福利，从贸易中获利的来源和大小，理解全球化的成本和效益。下面的paper代写范文继续进行讲述。

Abstract 
This paper develops an idea flows theory of trade and growth with heterogeneous firms. New firms learn from incumbent firms, but the diffusion technology ensures that entrants learn not just from frontier technologies, but from the entire technology distribution. By shifting the productivity distribution upwards, selection on productivity causes technology diffusion and this complementarity generates endogenous growth without scale effects. On the balanced growth path, the productivity distribution is a traveling wave with an increasing lower bound. Growth of the lower bound causes dynamic selection. Free entry mandates that trade liberalization increases the rates of technology diffusion and dynamic selection to offset the profits from new export opportunities. Consequently, trade integration raises longrun growth. The dynamic selection effect is a new source of gains from trade not found when firms are homogeneous. Calibrating the model implies that dynamic selection approximately triples the gains from trade relative to heterogeneous firm economies with static steady states. 

Introduction 
How does trade affect welfare? The sources and size of the gains from trade inform any discussion of either international or intra-national integration and shape our understanding of the costs and benefits of globalization.1 Building on the observation that only high performing firms participate in international trade (Bernard and Jensen 1995) recent work has studied the implications of firm heterogeneity for the gains from trade. The existence of substantial productivity differences between firms producing very similar products (Syverson 2011) introduces two channels for aggregate productivity gains that are absent when all firms produce on the technology frontier. First, cross-firm resource reallocation from less to more productive firms (Melitz 2003; Hsieh and Klenow 2009). 

Second, technology diffusion between firms (Luttmer 2007; Lucas and Moll 2013). Research on firm heterogeneity and trade has, with few exceptions, focused on the reallocation channel and studied economies with static steady states (Melitz 2003; Atkeson and Burstein 2010; Arkolakis, Costinot and Rodr´ıguez-Clare 2012; Melitz and Redding 2013).2 However, abstracting from technology diffusion overlooks a dynamic complementarity that exists between selection-induced reallocation and technology diffusion. Selection on productivity causes less productive firms to exit and shifts the productivity distribution of incumbent firms upwards. Whenever knowledge spillovers depend upon the entire distribution of technologies used in an economy, an upwards shift in the productivity distribution leads to technology diffusion. Thus, selection stimulates technology diffusion. 

This paper moves beyond static steady state economies and incorporates technology diffusion into a dynamic open economy with heterogeneous firms. The paper finds that firm heterogeneity matters for understanding the long run effects of trade because the combination of selection and technology diffusion creates a new channel through which trade increases growth and generates a new source of dynamic gains from trade. To formalize this argument I develop a dynamic version of Melitz (2003) featuring knowledge spillovers from incumbent firms to entrants. In most endogenous growth theory the source of growth is either knowledge spillovers that reduce the relative cost of entry in an expanding varieties framework (Romer 1990) or productivity spillovers that allow entrants to improve the frontier technology in a quality ladders framework (Aghion and Howitt 1992). However, Bollard, Klenow and Li (2013) find that entry costs do not fall relative to the cost of labor as economies grow. 

Moreover, the persistence of large within-industry productivity differences and the fact that most entrants do not use frontier technologies imply that not only innovation, but also the diffusion of existing technologies are important for aggregate productivity growth. Motivated by this observation recent work on idea flows has studied technology diffusion by assuming that agents can learn from meetings with other randomly chosen agents in an economy (Alvarez, Buera and Lucas 2008; Lucas and Moll 2013; Perla and Tonetti 2014). To model knowledge spillovers I build upon the idea flows literature by assuming that: (i) spillovers affect productivity, but not the cost of entry, and; (ii) spillovers depend not on the frontier technology, but upon the entire productivity distribution in an industry. 

To be specific, each firm has both a product and a process technology. Product ownership gives a firm monopoly rights over a particular variety and is protected by an infinitely lived patent.3 The firm’s process technology determines its productivity and is non-rival and partially non-excludable. When a new product is created, the entering firm adopts a process technology by learning from incumbent firms. In this manner knowledge about how to organize, manage and implement production diffuses between firms. However, learning frictions such as information asymmetries and adoption capacity constraints mean that not all entrants learn from the most productive firms. Instead, knowledge spillovers depend on the productivity of all active firms and spillovers increase as the distribution of incumbent firm productivity improves. 

This formalization of knowledge spillovers is consistent with evidence that the productivity distributions of entrants and incumbent firms move together over time (Aw, Chen and Roberts 2001; Foster, Haltiwanger and Krizan 2001; Disney, Haskel and Heden 2003). In the language of the Melitz model, the knowledge spillover process implies that instead of drawing from an exogenous distribution, entrants sample from a distribution that is endogenous to the productivity distribution of incumbent firms. Consequently, when selection increases the productivity cut-off below which firms exit, it also generates spillovers that shift upwards the productivity distribution of future entrants and lead to technology diffusion. 

Entry then causes further selection by raising industry competitiveness and making low productivity firms unprofitable. In equilibrium the positive feedback between selection and technology diffusion generates endogenous growth through dynamic selection. On the balanced growth path, the firm size distribution is stationary and the productivity distribution of incumbent firms is a traveling wave that shifts to the right over time as the exit cut-off rises.4 In the open economy firms face both fixed and variable trade costs. Only high productivity firms export and selection increases the exit cut-off and shifts the productivity distribution of incumbent firms to the right as in Melitz (2003). Consequently, trade liberalization generates technology diffusion and the expected productivity of future entrants rises. 

Unsurprisingly, this technology diffusion magnifies the rise in aggregate productivity following trade liberalization. More importantly, it leads to a permanent increase in the longrun growth rate. To understand why, consider the free entry condition. In equilibrium, the cost of entry must equal an entrant’s expected discounted lifetime profits. In the absence of technology diffusion, free entry mandates that an increase in expected profits from exporting is offset by a reduced probability of survival leading to the static selection effect found in Melitz (2003). However, with technology diffusion an increase in the level of the exit cut-off does not change the distribution of entrants’ productivity relative to the exit cut-off. Instead, I show that free entry requires an increase in the growth rate of the exit cut-off which raises the rate at which a successful entrant’s technology becomes obsolete and reduces entrants’ expected discounted lifetime profits.5 This dynamic selection effect increases the growth rate of average productivity and, consequently, consumption per capita. 

Thus, the complementarity between selection and technology diffusion implies that trade liberalization raises growth.6 How does higher growth affect the gains from trade? In static steady state economies that follow Melitz (2003) the equilibrium exit cut-off and export threshold are efficient, implying that any adjustments in their levels following changes in trade costs generate welfare gains absent from homogeneous firm models (Melitz and Redding 2013). However, Atkeson and Burstein (2010) find that these welfare gains are small relative to increases in average firm productivity since in general equilibrium the gains from selection and reallocation are offset by reductions in entry and technology investment. Similarly, Arkolakis, Costinot and Rodr´ıguezClare (2012) argue that firm heterogeneity is not important for quantifying the aggregate gains from trade. 

In particular, they show that in both Krugman (1980) and a version of Melitz (2003) with a Pareto productivity distribution, the gains from trade can be expressed as the same function of two observables: the import penetration ratio and the elasticity of trade with respect to variable trade costs (the trade elasticity). By raising the growth rate, the dynamic selection effect generates a new source of gains from trade that is not found in either static steady state economies with heterogeneous firms or dynamic economies with homogeneous firms. However, given the findings of Atkeson and Burstein (2010) and Arkolakis, Costinot and Rodr´ıguez-Clare (2012) it is natural to ask whether the benefits from an increase in the dynamic selection rate are offset by other general equilibrium effects.(paper代写)

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