Knowledge that Transforms

Observers of Silicon Valley's computer cluster report that employees move rapidly between competing firms, but evidence supporting this claim is scarce. Job-hopping is important in computer clusters because it facilitates the reallocation of talent and resources toward firms with superior innovations. Using new data on labor mobility, we find higher rates of job-hopping for college-educated men in Silicon Valley's computer industry than in computer clusters located out of the state. Mobility rates in other California computer clusters are similar to Silicon Valley's, suggesting some role for features of California law that make noncompete agreements unenforceable. Consistent with our model of innovation, mobility rates outside computer industries are no higher in California than elsewhere.

We link farmland values to climatic, soil, and socioeconomic variables for U.S. counties east of the 100th meridian, the historical boundary of agriculture not primarily dependent on irrigation. Degree days, a nonlinear transformation of the climatic variables suggested by agronomic experiments as more relevant to crop yield, gives an improved fit and increased robustness. Estimated coefficients are consistent with the experimental results. The model is employed to estimate the potential impacts on farmland values for a range of recent warming scenarios. The predictions are very robust, and more than 75% of the counties in our sample show a statistically significant effect, ranging from moderate gains to large losses, with losses in the aggregate that can become quite large under scenarios involving sustained heavy use of fossil fuels.

The U.S. retail trade sector underwent a massive restructuring and reallocation of activity in the 1990s with accompanying technological advances. Using a data set of establishments in that sector, we quantify and explore the relationship between this restructuring and reallocation and labor productivity dynamics. We find that virtually all of the labor productivity growth in the retail trade sector is accounted for by more productive entering establishments displacing much less productive exiting establishments. The productivity gap between low-productivity exiting single-unit establishments and entering high-productivity establishments from large, national chains plays a disproportionate role in these dynamics. Copyright by the President and Fellows of Harvard College and the Massachusetts Institute of Technology.

Analysis of patent citations is a core methodology in the study of knowledge diffusion. However, citations made by patent examiners have not been separately reported, adding unknown noise to the data. We leverage a recent change in the reporting of patent data showing citations added by examiners. The magnitude is high: two-thirds of citations on the average patent are inserted by examiners. Furthermore, 40% of all patents have all citations added by examiners. We analyze the distribution of examiner and inventor citations with respect to self-citation, distance, technology overlap, and vintage. Results indicate that inferences about inventor knowledge using pooled citations may suffer from bias or overinflated significance levels. Copyright by the President and Fellows of Harvard College and the Massachusetts Institute of Technology.

We investigate the implications of changes in the structure of the U.S. economy for monetary policy effectiveness. Estimating a vector autoregression over the pre- and post-1980 periods, we provide evidence of a reduced effect of monetary policy shocks in the latter period. We estimate a structural model that replicates well the economy's response in both periods, and perform counterfactual experiments to determine the source of the change in the monetary transmission mechanism and in the economy's volatility. We find that by responding more strongly to inflation expectations, monetary policy has stabilized the economy more effectively in the post-1980 period.

This paper examines the properties of instrumental variables (IV) applied to models with essential heterogeneity, that is, models where responses to interventions are heterogeneous and agents adopt treatments (participate in programs) with at least partial knowledge of their idiosyncratic response. We analyze two-outcome and multiple-outcome models, including ordered and unordered choice models. We allow for transition-specific and general instruments. We generalize previous analyses by developing weights for treatment effects for general instruments. We develop a simple test for the presence of essential heterogeneity. We note the asymmetry of the model of essential heterogeneity: outcomes of choices are heterogeneous in a general way; choices are not. When both choices and outcomes are permitted to be symmetrically heterogeneous, the method of IV breaks down for estimating treatment parameters.

This paper empirically analyzes economic and noneconomic determinants of individual attitudes toward immigrants, within and across countries. The two survey data sets used, covering a wide range of developed and developing countries, make it possible to test for interactive effects between individual characteristics and country-level attributes. In particular, theory predicts that the correlation between pro-immigration attitudes and individual skill should be related to the skill composition of natives relative to immigrants in the destination country. Skilled individuals should favor immigration in countries where natives are more skilled than immigrants and oppose it otherwise. Results based on direct and indirect measures of the relative skill composition are consistent with these predictions. Noneconomic variables also are correlated with immigration attitudes, but they don't alter significantly the labor-market results.

Although economists have long been aware of Jensen's inequality, many econometric applications have neglected an important implication of it: under heteroskedasticity, the parameters of log-linearized models estimated by OLS lead to biased estimates of the true elasticities. We explain why this problem arises and propose an appropriate estimator. Our criticism of conventional practices and the proposed solution extend to a broad range of applications where log-linearized equations are estimated. We develop the argument using one particular illustration, the gravity equation for trade. We find significant differences between estimates obtained with the proposed estimator and those obtained with the traditional method.