Assistant Professor of Economics, Tufts University
The Global Spatial Distribution of Economic Activity: Nature, History, and the Role of Trade (with Vernon Henderson, Tim Squires and David N. Weil; revision requested, Quarterly Journal of Economics)Abstract: We study the distribution of economic activity, as proxied by lights at night, across 250,000 grid cells of average area 560 square kilometers. We first document that nearly half of the variation can be explained by a parsimonious set of physical geography attributes. A full set of country indicators only explains a further 10%. When we divide geographic characteristics into two groups, those primarily important for agriculture and those primarily important for trade, we find that the agriculture variables have relatively more explanatory power in countries that developed early and the trade variables have relatively more in countries that developed late, despite the fact that the latter group of countries are far more dependent on agriculture today. We explain this apparent puzzle in a model in which two technological shocks occur, one increasing agricultural productivity and the other decreasing transportation costs, and in which agglomeration economies lead to persistence in urban locations. In countries that developed early, structural transformation due to rising agricultural productivity began at a time when transport costs were still relatively high, so urban agglomerations were localized in agricultural regions. When transport costs fell, these local agglomerations persisted. In late-developing countries, transport costs fell well before structural transformation. To exploit urban scale economies, manufacturing agglomerated in relatively few, often coastal, locations. With structural transformation, these initial coastal locations grew, without formation of more cities in the agricultural interior.
The Heterogeneous Effects of Transportation Investments: Evidence from sub-Saharan Africa 1960-2010 (with Rémi Jedwab; available upon request)
Abstract: Previous work on the effects of transportation investments has focused on estimating average impacts in middle and high income countries. Less is known about the heterogeneity of the impact of these investments, depending on the context in which they take place. We shed light on this by studying how the effects of transportation investments vary as a function of the characteristics of the places they connect. Using new data on roads and cities spanning over 50 years in 39 African countries, we document the effect of road construction on city population growth, through the channel of increasing market access. First, using changes in market access due to distant road construction as a source of exogenous variation in market access, we estimate a 30-year elasticity of city population with respect to market access of 0.05 to 0.20, larger than an OLS estimate of 0.035, but smaller than estimates for other contexts. Second, relying on the same identification strategy, we find suggestive evidence that it is stronger for small and remote cities, and cities that experience a large change in their market access, especially to other cities of the same country or international ports, and weaker for cities in areas with a comparative advantage in agriculture and areas most likely to be favored by ethnic patronage. The observed heterogeneity in the effects confirms the importance of understanding local context when evaluating the impact of transport investment.
Abstract: Transport investment has played an important role in the economic development of many countries. Starting from a low base, African countries have recently initiated several massive transportation infrastructure projects. However, surprisingly little is known about the current levels, past evolution, and correlates of transportation infrastructure in Africa. In this paper, we introduce a new data set on the evolution of the stocks of railroads (1862-2015) and multiple types of roads (1960-2015) for 43 sub-Saharan African countries. First, we compare our estimates with those from other available data sets, such as the World Development Indicators. Second, we document the aggregate evolution of transportation investments over the past century in Africa. We confirm that railroads were a ``colonial'' transportation technology, whereas paved roads were mostly a ``post-colonial'' technology. We also highlight how investment patterns have followed economic patterns, thus suggesting the pro-cyclicality of transportation investments. Third, we report conditional correlations between 5-year infrastructure growth and several geographic, economic and political factors during the period 1960-2015. We find strong correlations between transportation investments and economic development as well as more political factors including pre-colonial centralization, ethnic fractionalization, European settlement, and democracy. This suggests that non-economic factors may also have a significant role in the ability of countries to invest in, and maintain, these public goods.
Is urbanization in sub-Saharan Africa different?(with Vernon Henderson and Mark Roberts)Abstract: In the past dozen years, a literature has developed arguing that urbanization has unfolded differently in post-independence sub-Saharan Africa than in the rest of the developing world, with implications for African economic growth overall. While African countries are more urbanized than other countries at comparable levels of income, it is well-recognized that total and sector GDP data are of very low quality, especially in Africa. When viewed from the perspective of effective technology as suggested in endogenous growth frameworks (and as proxied by educational attainment), the African urbanization experience overall matches global patterns. There are differences, however, at a sector level. Agricultural trade price shocks have a differential effect in Africa, but not what is postulated in some of the literature. In our data, shocks that improve farm prices deter African urbanization, as might be expected in simple two sector models. In the remainder of the developing world, such shocks promote urbanization. The paper explores potential reasons for this difference, looking, in particular, at differences in land ownership institutions and the likelihood of agricultural surpluses being invested in urban production. Shocks to modern manufacturing spur urbanization in the rest of the developing world, but effects are dependent on the level of development and implied ability to accommodate the shocks. Thus many countries in Africa, with their lower level of development, do not respond to these shocks. Finally, historical indicators of the potential for good institutions promote urbanization both inside and outside of Africa.
Has climate change driven urbanization in Africa? (2017; with Vernon Henderson and Uwe Deichmann; formerly "50 years of urbanization in Africa: Examining the role of climate") Journal of Development Economics 124: 60-82. (ungated version)
Abstract: This paper documents strong but differentiated links between climate and urbanization in large panels of districts and cities in Sub-Saharan Africa, which has dried substantially in the past fifty years. The key dimension of heterogeneity is whether cities are likely to have manufacturing for export outside their regions, as opposed to being exclusively market towns providing local services to agricultural hinterlands. In regions where cities are likely to be manufacturing centers (25% of our sample), drier conditions increase urbanization and total urban incomes. There, urban migration provides an "escape" from negative agricultural moisture shocks. However, in the remaining market towns (75% of our sample), cities just service agriculture. Reduced farm incomes from negative shocks reduce demand for urban services and derived demand for urban labor. There, drying has little impact on urbanization or total urban incomes. Lack of structural transformation in Africa inhibits a better response to climate change.
- Stata data and code for producing final regression tables
- ArcGIS and Stata code and input data of various types for producing the stata data above
The View from Above: Applications of Satellite Data in Economics (2016; with Dave Donaldson) Journal of Economic Perspectives 30(4): 171-198.Abstract: The past decade or so has seen a dramatic change in the way that economists can learn by watching our planet from above. A revolution has taken place in remote sensing and allied fields such as computer science, engineering, and geography. Petabytes of satellite imagery have become publicly accessible at increasing resolution, many algorithms for extracting meaningful social science information from these images are now routine, and modern cloud-based processing power allows these algorithms to be run at global scale. This paper seeks to introduce economists to the science of remotely sensed data, and to give a flavor of how this new source of data has been used by economists so far and what might be done in the future.
Farther on down the road: transport costs, trade and urban growth (2016) Review of Economic Studies 83(3): 1263-1295. (ungated version)
Abstract: How does isolation affect the economic activity of cities? Transport costs are widely considered an important barrier to local economic activity but their impact in developing countries is not well-studied. This paper investigates the role of inter-city transport costs in determining the income of sub-Saharan African cities. In particular, focusing on fifteen countries whose largest city is a port, I ask how important access to that city is for the income of hinterland cities. The lack of panel data on both local economic activity and transport costs has prevented rigorous empirical investigation of this question. I fill this gap with two new datasets. Satellite data on lights at night proxy for city economic activity, and new road network data allow me to calculate the shortest route between cities. Cost per unit distance is identified by plausibly exogenous world oil prices. The results show that an oil price increase of the magnitude experienced between 2002 and 2008 induces the income of cities near a major port to increase by 6.6 percent relative to otherwise identical cities one standard deviation farther away. Combined with external estimates, this implies an elasticity of city economic activity with respect to transport costs of -0.25 at that distance. Moreover, the effect differs by the surface of roads between cities. Cities connected to the port by paved roads are chiefly affected by transport costs to the port, while cities connected to the port by unpaved roads are more affected by connections to secondary centers.
Dowry Deaths: response to weather variability in India (2014; with Sheetal Sekhri) Journal of Development Economics 111: 212-223. (ungated version)
Abstract: We examine the effect of rainfall shocks on dowry deaths using data from 583 Indian districts for 2002-2007. We find that a one standard deviation decline in annual rainfall from the local mean increases reported dowry deaths by 7.8 percent. Wet shocks have no apparent effect. We examine patterns of other crimes to investigate if increase in general unrest during economic downturn explains the results but do not find supportive evidence. Women's political representation in the national parliament has no apparent mitigating effect on dowry deaths.
Media coverage:Calcutta Telegraph, Mint [India], The Hindu [India]
Abstract: We develop a statistical framework to use satellite data on night lights to augment official income growth measures. For countries with poor national income accounts, the optimal estimate of growth is a composite with roughly equal weights on conventionally measured growth and growth predicted from lights. Our estimates differ from official data by up to three percentage points annually. Using lights, empirical analyses of growth need no longer use countries as the unit of analysis; we can measure growth for sub- and supra-national regions.
Media coverage:Broadcast: Reuters Video, Bloomberg Television
Global trends in emerging infectious diseases (2008; with Kate E. Jones, Nikkita G. Patel, Marc A. Levy, Deborah Balk, John L. Gittleman and Peter Daszak), Nature 451: 990-993.
Abstract: Emerging infectious diseases (EIDs) are a significant burden on global economies and public health. Their emergence is thought to be driven largely by socio-economic, environmental and ecological factors, but no comparative study has explicitly analysed these linkages to understand global temporal and spatial patterns of EIDs. Here we analyse a database of 335 EID 'events' (origins of EIDs) between 1940 and 2004, and demonstrate non-random global patterns. EID events have risen significantly over time after controlling for reporting bias, with their peak incidence (in the 1980s) concomitant with the HIV pandemic. EID events are dominated by zoonoses (60.3% of EIDs): the majority of these (71.8%) originate in wildlife (for example, severe acute respiratory virus, Ebola virus), and are increasing significantly over time. We find that 54.3% of EID events are caused by bacteria or rickettsia, reflecting a large number of drug-resistant microbes in our database. Our results confirm that EID origins are significantly correlated with socio-economic, environmental and ecological factors, and provide a basis for identifying regions where new EIDs are most likely to originate (emerging disease 'hotspots'). They also reveal a substantial risk of wildlife zoonotic and vector-borne EIDs originating at lower latitudes where reporting effort is low. We conclude that global resources to counter disease emergence are poorly allocated, with the majority of the scientific and surveillance effort focused on countries from where the next important EID is least likely to originate.
Supplementary Information (ungated)
Media coverage:Broadcast: National Public RadioPrint: NBC News, The Times [U. K.], Reuters India, U.S. News & World Report, The Telegraph [U.K.]
SELECTED WORK IN PROGRESS
Accessibility and mobility in urban India (with Prottoy Akbar, Victor Couture, and Gilles Duranton)