Knowledge that Transforms

Little is known about the impacts of military service on human capital and labor market outcomes due to an absence of data as well as sample selection: recruits are self-selected, screened, and selectively survive. We examine the case of Uganda, where rebel recruitment methods provide exogenous variation in conscription. Economic and educational impacts are widespread and persistent: schooling falls by nearly a year, skilled employment halves, and earnings drop by a third. Military service seems to be a poor substitute for schooling. Psychological distress is evident among those exposed to severe war violence and is not limited to ex-combatants.

Conventional wisdom in economic history suggests that conflict between countries can be enormously disruptive of economic activity, especially international trade. We study the effects of war on bilateral trade with available data extending back to 1870. Using the gravity model, we estimate the contemporaneous and lagged effects of wars on the trade of belligerent nations and neutrals, controlling for other determinants of trade, as well as the possible effects of reverse causality. We find large and persistent impacts of wars on trade, national income, and global economic welfare. We also conduct a general equilibrium comparative statics exercise that indicates costs associated with lost trade might be at least as large as the conventionally measured direct costs of war, such as lost human capital, as illustrated by case studies of World Wars I and II.

This paper examines the role of migration networks in determining self-selection patterns of Mexico-U.S. migration. A simple theoretical framework shows the impact of networks on migration incentives at different education levels and how this affects the composition of migrant skills. Empirically, we find positive or education-neutral selection in communities with weak migrant networks but negative self-selection in communities with stronger networks. This is consistent with high migration costs driving positive or intermediate self-selection, as advocated by Chiquiar and Hanson (2005), and with negative self-selection being driven by lower returns to education in the United States than in Mexico, as advocated by Borjas (1987).

We determine how time delays affect trade, using newly collected data on the days it takes to move standard cargo from the factory gate to the ship in 98 countries. We estimate a difference gravity equation and find that each additional day that a product is delayed prior to being shipped reduces trade by more than 1%. Put differently, each day is equivalent to a country distancing itself from its trade partners by about 70 km on average. We also find that delays have a relatively greater impact on exports of time-sensitive goods, such as perishable agricultural products.

We develop a new estimator of the number of factors in the approximate factor models. The estimator works well even when the idiosyncratic terms are substantially correlated. It is based on the fact, established in the paper, that any finite number of the largest “idiosyncratic” eigenvalues of the sample covariance matrix cluster around a single point. In contrast, all the “systematic” eigenvalues, the number of which equals the number of factors, diverge to infinity. The estimator consistently separates the diverging eigenvalues from the cluster and counts the number of the separated eigenvalues. We consider a macroeconomic and a financial application.

We use policy discontinuities at state borders to identify the effects of minimum wages on earnings and employment in restaurants and other low-wage sectors. Our approach generalizes the case study method by considering all local differences in minimum wage policies between 1990 and 2006. We compare all contiguous county pairs in the United States that straddle a state border and find no adverse employment effects. We show that traditional approaches that do not account for local economic conditions tend to produce spurious negative effects due to spatial heterogeneities in employment trends that are unrelated to minimum wage policies. Our findings are robust to allowing for long-term effects of minimum wage changes.

Precautionary saving has been linked to the property of prudence, and the property of temperance has been used to show how the presence of an unavoidable risk affects one's behaviour towards a second risk. These two higher order risk effects also play key roles in aversion to negative skewness and to kurtosis, respectively. This article presents a laboratory experiment to determine whether subjects are prudent and/or temperate. The experiment is based upon preferences over lottery pairs in simple 50–50 gambles. Subjects are asked in which of two states of nature they would prefer to receive a zero-mean gamble. For prudence, the choices are between a lower and higher wealth outcome. For temperance, the choices are between a state with no other risk and a state with a second (independent) risk. The results show behavioural evidence for prudence, but they also show evidence of intemperate behaviour. Implications of these results for both expected-utility and non-expected-utility models are examined.