In this paper, I examine the relationship between increasing returns to scale and the geographic concentration of economic activity. Using data on U.S. counties, I estimate the structural parameters of the Krugman (1991) model of economic geography. The specification I use, which is derived from...

Whether the danger invoked is nuclear war or genetically modified foods, far more people in some countries than in others say they are afraid. Using data from six surveys, I show that the levels of reported fear of different dangers correlate strongly across both individuals and countries. I...

In this paper, I develop a new identification method to solve the problem of simultaneous equations, based on heteroskedasticity of the structural shocks. I show that if the heteroskedasticity can be described as a two-regime process, then the system is just identified under relatively weak...

We propose and evaluate a technique for instrumental variables estimation of linear models with conditional heteroskedasticity. The technique uses approximating parametric models for the projection of right hand side variables onto the instrument space, and for conditional heteroskedasticity and...

We apply a new estimator to the measurement of the economic returns to education. We control for endogenous education, unobserved ability and measurement error using only the natural heteroscedasticty of wages and education attainment. Our prefered estimate, 6.07%, is closer to the OLS estimate...

In recent empirical literature on spatial agglomeration, many papers find evidence consistent with location-specific externalities of some sort. Our willingness to accept evidence of agglomeration economies depends on how well key estimation problems have been addressed. Three issues are...

We consider a model with several regions whose technological ability and factor endowments are identical and in which transport costs between regions are non-negligible. Nonetheless, certain goods are sometimes produced by multiple firms all of which are located in the same region. These goods...

When economic activity is concentrated over space or over time, it is more efficient. Most production occurs in geographic hot spots, and most production occurs between 9 and 12 in the morning and 1 to 5 in the afternoon on weekdays. The thick-market efficiencies that encourage the concentration...