Benjamin Moll

Knowledge Growth and the Allocation of Time

We analyze a model economy with many agents, each with a different productivity level. Agents divide their time between two activities: producing goods with the production-related knowledge they already have and interacting with others in search of new, productivity-increasing ideas. These choices jointly determine the economy’s current production level and its rate of learning and real growth. We construct the balanced growth path for this economy. We also study the allocation chosen by an idealized planner who takes into account and internalizes the external benefits of search. Finally, we provide three examples of alternative learning technologies and show that the properties of equilibrium allocations are quite sensitive to two of these variations.

Partial differential equation models in macroeconomics

The purpose of this article is to get mathematicians interested in studying a number of partial differential equations (PDEs) that naturally arise in macroeconomics. These PDEs come from models designed to study some of the most important questions in economics. At the same time, they are highly interesting for mathematicians because their structure is often quite difficult. We present a number of examples of such PDEs, discuss what is known about their properties, and list some open questions for future research.

Controlling a Distribution of Heterogeneous Agents

This paper analyzes the problem of a benevolent planner wishing to control a population of heterogeneous agents subject to idiosyncratic shocks. This is equivalent to a deterministic control problem in which the state variable is the cross-sectional distribution. We show how, in continuous time, this problem can be broken down into a dynamic programming equation plus the law of motion of the distribution, and we introduce a new numerical algorithm to solve it. As an application, we analyze the constrained-efficient allocation of an Aiyagari economy with a fat-tailed wealth distribution. We fi nd that the constrained-efficient allocation features more wealth inequality than the competitive equilibrium.

Life Cycle Wage Growth across Countries

This paper documents how life cycle wage growth varies across countries. We harmonize repeated cross-sectional surveys from a set of countries of all income levels and then measure how wages rise with potential experience. Our main finding is that experience-wage profiles are on average twice as steep in rich countries as in poor countries. In addition, more educated workers have steeper profiles than the less educated; this accounts for around one-third of cross-country differences in aggregate profiles. Our findings are consistent with theories in which workers in poor countries accumulate less human capital or face greater search frictions over the life cycle.

Life-Cycle Human Capital Accumulation Across Countries: Lessons From U.S. Immigrants

This paper assesses cross-country variation in life-cycle human capital accumulation, using new evidence from US immigrants. The returns to experience accumulated in an immigrant’s birth country before migrating are positively correlated with birth-country GDP per capita. To understand this fact, we build a model of life-cycle human capital accumulation that features three potential theories: differential human capital accumulation, differential selection, and differential skill loss. We use new data on the characteristics of immigrants and nonmigrants from a large set of countries to distinguish between these theories. The most likely theory is that immigrants from poor countries accumulate less human capital in their birth countries before migrating. Our findings imply that life-cycle human capital stocks are much larger in rich countries.

Economic development, flow of funds, and the equilibrium interaction of financial frictions

Significance Variation in the type of financial frictions faced by households and firms is an overlooked dimension of regional heterogeneity that has the potential to explain cross-regional factor flows and differences in concentration of economic activity. Our research combines a theoretical model with a complexity and variety of data from Thailand. The theoretical model features variation in financial regimes, moral hazard, and limited commitment, inferred from the data. In a counterfactual experiment we explore the effects of protecting wages in urban areas from incoming migrants and protecting rural areas from capital outflow. Economic life in cities would suffer enormously, as would rural and national productivity, with an increase in overall inequality. We use a variety of different datasets from Thailand to study not only the extremes of micro and macro variables but also within-country flow of funds and labor migration. We develop a general equilibrium model that encompasses regional variation in the type of financial friction and calibrate it to measured variation in regional aggregates. The model predicts substantial capital and labor flows from rural to urban areas even though these differ only in the underlying financial regime. Predictions for micro variables not used directly provide a model validation. Finally, we estimate the impact of a policy of counterfactual, regional isolationism.

When Inequality Matters for Macro and Macro Matters for Inequality

We develop an efficient and easy to use computational method for solving a wide class of general equilibrium heterogeneous agent models with aggregate shocks together with an open source suite of codes that implement our algorithms in an easy to use toolbox. Our method extends standard linearization techniques and is designed to work in cases when inequality matters for the dynamics of macroeconomic aggregates. We present two applications that analyze a two asset incomplete markets model parameterized to match the distribution of income, wealth, and marginal propensities to consume. First, we show that our model is consistent with two key features of aggregate consumption dynamics that are difficult to match with representative agent models: (1) the sensitivity of aggregate consumption to predictable changes in aggregate income, and (2) the relative smoothness of aggregate consumption. Second, we extend the model to feature capital-skill complementarity and show how factor-specific productivity shocks shape dynamics of income and consumption inequality.