The prevalence of many urban phenomena changes systematically with population size1. We propose a theory that unifies models of economic complexity2,3 and cultural evolution4 to derive urban scaling. The theory accounts for the difference in scaling exponents and average prevalence across phenomena, as well as the difference in the variance within phenomena across cities of similar size. The central ideas are that a number of necessary complementary factors must be simultaneously present for a phenomenon to occur, and that the diversity of factors is logarithmically related to population size. The model reveals that phenomena that require more factors will be less prevalent, scale more superlinearly and show larger variance across cities of similar size. The theory applies to data on education, employment, innovation, disease and crime, and it entails the ability to predict the prevalence of a phenomenon across cities, given information about the prevalence in a single city.
This article, in an effort to assist the selection and deployment of evidence-informed strategies, proposes a new conceptual framework for responding to community violence among youth. First, the phenomenon of community violence is understood in context using a new violence typology organized along a continuum. Second, the need for a new anti-community violence framework is established. Third, a framework is developed, blending concepts from the fields of public safety and public health. Fourth, evidence from systematic reviews and meta-analyses concerning community violence is summarized and categorized. Finally, an anti-violence framework populated with evidence-informed strategies is presented and discussed.
Social relations involve both face-to-face interaction as well as telecommunications. We can observe the geography of phone calls and of the mobility of cell phones in space. These two phenomena can be described as networks of connections between different points in space. We use a dataset that includes billions of phone calls made in Colombia during a six-month period. We draw the two networks and find that the call-based network resembles a higher order aggregation of the mobility network and that both are isomorphic except for a higher spatial decay coefficient of the mobility network relative to the call-based network: when we discount distance effects on the call connections with the same decay observed for mobility connections, the two networks are virtually indistinguishable.
The paper studies the nature and extent of Egyptian "crony" capitalism by comparing the corporate performance and the stock market valuation of politically connected and unconnected firms, before and after the 2011 popular uprising that led to the end of President Mubarak 30 years rule. First, we identify politically connected firms and conduct an event study around the events of 2011, as well as around previous events related to rumors about Mubarak’s health. We estimate the market valuation of political connections to be 20% to 23% of the value of connected firms. Second, we explore the mechanisms used for granting these privileges by looking at corporate behavior before 2011. It appears that these advantages allowed connected firms to increase their market size and power and their borrowings. We finally compare the performance of firms and find that the rate of return on assets of connected firms was lower than that of non-connected firms by nearly 3 percentage points. We argue that this indicates that the granting of privileges was not part of a successful industrial policy but instead, that it led to a large misallocation of capital towards less efficient firms, which together with reduced competition, led to lower economic growth.
Aim of this paper is to introduce the complex system perspective into retail market analysis. Currently, to understand the retail market means to search for local patterns at the micro level, involving the segmentation, separation and profiling of diverse groups of consumers. In other contexts, however, markets are modelled as complex systems. Such strategy is able to uncover emerging regularities and patterns that make markets more predictable, e.g. enabling to predict how much a country’s GDP will grow. Rather than isolate actors in homogeneous groups, this strategy requires to consider the system as a whole, as the emerging pattern can be detected only as a result of the interaction between its self-organizing parts. This assumption holds also in the retail market: each customer can be seen as an independent unit maximizing its own utility function. As a consequence, the global behaviour of the retail market naturally emerges, enabling a novel description of its properties, complementary to the local pattern approach. Such task demands for a data-driven empirical framework. In this paper, we analyse a unique transaction database, recording the micro-purchases of a million customers observed for several years in the stores of a national supermarket chain. We show the emergence of the fundamental pattern of this complex system, connecting the products’ volumes of sales with the customers’ volumes of purchases. This pattern has a number of applications. We provide three of them. By enabling us to evaluate the sophistication of needs that a customer has and a product satisfies, this pattern has been applied to the task of uncovering the hierarchy of needs of the customers, providing a hint about what is the next product a customer could be interested in buying and predicting in which shop she is likely to go to buy it.
We propose and implement a new technique for measuring the total magnitude of a growth episode: the change in output per capita resulting from one structural break in the trend growth of output (acceleration or deceleration) to the next. The magnitude of the gain or loss from a growth episode combines (a) the difference between the post-break growth rate versus a counter-factual "no break" growth rate and (b) the duration of the episode to estimate the difference in output per capita at the end of an episode relative to what it would have been in the "no break" scenario. We use three "counter-factual" growth rates that allow for differing degrees of regression to global average growth: "no change" (zero regression to the mean), "world episode average" (full regression to the mean) and "unconditional predicted growth" (which uses a regression for each growth episode to predict future growth based only on past growth and episode initial level). We can also calculate the net present value at the start of an episode of the gain or loss in output comparing the actual evolution of output per capita versus a counter-factual. This method allows us to place dollar figures on growth episodes. The top 20 growth accelerations have Net Present Value (NPV) magnitude of 30 trillion dollars - twice US GDP. Conversely, the collapse in output in Iran between 1976 and 1988 produced an NPV loss of $143,000 per person. The top 20 growth decelerations account for 35 trillion less in NPV of output. Paraphrasing Lucas, once one begins to think about what determines growth events that cause the appearance or disappearance of output value equal to the total US economy, it is hard to think about anything else.
We study the structure of international aid coordination by creating and analyzing a tripartite network of donor organizations, recipient countries and development issues using web-based information. We develop a measure of coordination and find that it is moderate, achieving about 60% of its theoretical maximum. Many countries are strongly connected to organizations that are related to the issues that are salient there. Nevertheless, we identify many countries that are poorly served, issues that are inadequately attended to, and organizations that focus on the wrong combination of places and issues. Our approach may be used to improve decentralized coordination.
In economic systems, the mix of products that countries make or export has been shown to be a strong leading indicator of economic growth. Hence, methods to characterize and predict the structure of the network connecting countries to the products that they export are relevant for understanding the dynamics of economic development. Here we study the presence and absence of industries in international and domestic economies and show that these networks are significantly nested. This means that the less filled rows and columns of these networks' adjacency matrices tend to be subsets of the fuller rows and columns. Moreover, we show that their nestedness remains constant over time and that it is sustained by both, a bias for industries that deviate from the networks' nestedness to disappear, and a bias for the industries that are missing according to nestedness to appear. This makes the appearance and disappearance of individual industries in each location predictable. We interpret the high level of nestedness observed in these networks in the context of the neutral model of development introduced by Hidalgo and Hausmann (2009). We show that the model can reproduce the high level of nestedness observed in these networks only when we assume a high level of heterogeneity in the distribution of capabilities available in countries and required by products. In the context of the neutral model, this implies that the high level of nestedness observed in these economic networks emerges as a combination of both, the complementarity of inputs and heterogeneity in the number of capabilities available in countries and required by products. The stability of nestedness in industrial ecosystems, and the predictability implied by it, demonstrates the importance of the study of network properties in the evolution of economic networks.
We show that world trade network datasets contain empirical evidence that the dynamics of innovation in the world economy indeed follows the concept of creative destruction, as proposed by J.A. Schumpeter more than half a century ago. National economies can be viewed as complex, evolving systems, driven by a stream of appearance and disappearance of goods and services. Products appear in bursts of creative cascades. We find that products systematically tend to co-appear, and that product appearances lead to massive disappearance events of existing products in the following years. The opposite–disappearances followed by periods of appearances–is not observed. This is an empirical validation of the dominance of cascading competitive replacement events on the scale of national economies, i.e., creative destruction. We find a tendency that more complex products drive out less complex ones, i.e., progress has a direction. Finally we show that the growth trajectory of a country’s product output diversity can be understood by a recently proposed evolutionary model of Schumpeterian economic dynamics.
Much of the analysis of economic growth has focused on the study of aggregate output. Here, we deviate from this tradition and look instead at the structure of output embodied in the network connecting countries to the products that they export. We characterize this network using four structural features: the negative relationship between the diversification of a country and the average ubiquity of its exports, and the non-normal distributions for product ubiquity, country diversification and product co-export. We model the structure of the network by assuming that products require a large number of non-tradable inputs, or capabilities, and that countries differ in the completeness of the set of capabilities they have. We solve the model assuming that the probability that a country has a capability and that a product requires a capability are constant and calibrate it to the data to find that it accounts well for all of the network features except for the heterogeneity in the distribution of country diversification. In the light of the model, this is evidence of a large heterogeneity in the distribution of capabilities across countries. Finally, we show that the model implies that the increase in diversification that is expected from the accumulation of a small number of capabilities is small for countries that have a few of them and large for those with many. This implies that the forces that help drive divergence in product diversity increase with the complexity of the global economy when capabilities travel poorly.
Anyone who undertakes to produce a volume of surveys in economic development must confront the question: Does the world really need another one? The field changes over time and, one hopes, knowledge accumulates. So, one motive is the desire to cover the more recent advances. And indeed, economic development has been one of the most dynamic and innovative fields within economics in recent years. While one primary goal is to inform policy makers, it also hoped that the volume will assist scholars in designing research agendas that are informed by policy questions, in particular, by the gaps in knowledge that would speak to major policy issues. The development field has always been one in which the worlds of research and practice are in close relationship with each other and move in tandem. The large number of PhD economists who work in international organizations such as the World Bank and the influence of academia among developing-country officialdom ensure that ideas emanating from the ivory tower often find quick application. But equally important, in principle, is the reverse feedback—the need to tilt researchers' attention on the questions that are, or should be, on the policy agenda. The organization of the present volume around policy issues is designed to make a contribution toward both of these goals.
Development economists should stop acting as categorical advocates (or detractors) for specific approaches to development. They should instead be diagnosticians, helping decisionmakers choose the right model (and remedy) for their specific realities, among many contending models (and remedies). In this spirit, Ricardo Hausmann, Andres Velasco, and I have developed a "growth diagnostics" framework that sketches a systematic process for identifying binding constraints and prioritizing policy reforms in multilateral agencies and bilateral donors. Growth diagnostics is based on the idea that not all constraints bind equally and that a sensible and practical strategy consists of identifying the most serious constraint(s) at work. The practitioner works with a decision tree to do this. The second step in growth diagnostics is to identify remedies for relaxing the constraint that are appropriate to the context and take cognizance of potential second-best complications. Successful countries are those that have implemented these two steps in an ongoing manner: identify sequentially the most binding constraints and remove them with locally suited remedies. Diagnostics requires pragmatism and eclecticism, in the use of both theory and evidence. It has no room for dogmatism, imported blueprints, or empirical purism.
For Adam Smith, wealth was related to the division of labor. As people and firms specialize in different activities, economic effi- ciency increases, suggesting that development is associated with an increase in the number of individual activities and with the complexity that emerges from the interactions between them. Here we develop a view of economic growth and development that gives a central role to the complexity of a country’s economy by interpreting trade data as a bipartite network in which countries are connected to the products they export, and show that it is possible to quantify the complexity of a country’s economy by characterizing the structure of this network. Furthermore, we show that the measures of complexity we derive are correlated with a country’s level of income, and that deviations from this relationship are predictive of future growth. This suggests that countries tend to converge to the level of income dictated by the complexity of their productive structures, indicating that development efforts should focus on generating the conditions that would allow complexity to emerge to generate sustained growth and prosperity.
El Salvador is a star reformer. After the civil war of the 1980s, the country was able to adopt important political and institutional reforms. These included the incorporation of all political groups into the electoral process, the adoption of a new constitution, the elimination of the military police, the creation of a civilian police with members from both sides of the war, and the adoption of rules to strengthen the independence of the judiciary. On the economic front, the country consolidated its fiscal position, modernized its tax system, liberalized trade and banking, improved the regulation and supervision of its financial system, privatized most state productive assets including energy and telecommunications, and reformed its social security system in line with the Chilean model. It also expanded and granted local autonomy to the school system through the Community-Managed Schools Program (EDUCO). Finally, El Salvador dollarized its financial system in November 2000. Given the investment-grade rating earned by the country, domestic money market rates have converged to U.S. levels.
Unfortunately, El Salvador is not a star performer. Standard theory would predict that such an improvement in the institutional and regulatory environment should be followed by convergence to a higher income level. Instead, after an initial period of recovery that lasted until 1997, real gross national income per capita stagnated at levels comparable to those achieved by the country in the late 1970s. Its income relative to the United States has not recovered from the fall associated with the civil war and is just over half the ratio achieved in the late 1970s.
El Salvador is not alone in finding that reform efforts have had smaller-thanexpected growth effects. With the exception of Chile, the effects of reform ongrowth throughout Latin America have been smaller than the initial estimates carried out in the mid-1990s.In this context, El Salvador is an interesting case, since it has been particularly effective in applying wide-ranging reforms.
This paper explores why these reforms have failed to produce more growth and what can be done about it.2 We begin by placing the economic choices faced by the incoming Salvadoran administration in a regional and historical perspective. The late 1980s and early 1990s in Latin America were preceded by a decade of stagnation, but coincided with a time of unusual confidence in the future. The collapse of communism, the failure of many interventionist policies in Latin America in the 1980s, and Chile’s success gave governments a clear idea of the road they wanted to leave and the road they wanted to take. Inadequate past performance and consensus on the road ahead led to a forceful policy agenda.