U.S. inequality: Debt constraints or incomplete asset markets?

To examine the role of debt constraints and incomplete asset markets (lack of insurance markets) in explaining U.S. inequality, we run horse races between competing models. For a widely used model, we decompose inequality into its fundamental driving forces. The underlying source of inequality in all models is uninsurable idiosyncratic risk. Both debt constraints and incomplete asset markets are needed to account for inequality, but asset market incompleteness is the key friction. It better accounts for the concentration and dispersion of wealth, and is the most costly friction in terms of welfare. Tight debt constraints are important for explaining the lower tail of the wealth distribution.     

Aggregate implications of micro asset market segmentation

An extensive empirical literature finds that micro asset markets are segmented from one another. We develop a consumption-based asset pricing model to quantify the aggregate implications of a financial system comprised of many such segmented micro asset markets. We specify exogenously the level of segmentation that determines how much idiosyncratic risk traders bear in their micro market and calibrate the segmentation to match facts about systematic and idiosyncratic return volatility. In our benchmark model traders bear 30% of their idiosyncratic risk, the unconditional aggregate equity premium is 2.4% annual, and the welfare costs of segmentation are substantial, 1.8% of lifetime consumption.     

Asset Pricing with Limited Risk Sharing and Heterogeneous Agents

We develop a model with incomplete markets and heterogeneousagents that generates a large equity premium, while simultaneouslymatching stock market participation and individual asset holdings.The high risk-premium is driven by incomplete risk sharing amongstockholders, which results from the combination of aggregateuncertainty, borrowing constraints, and a (realistically) calibratedlife-cycle earnings profile subject to idiosyncratic shocks.We show that it is challenging to simultaneously match assetpricing moments and individual portfolio decisions, while limitedparticipation has a negligible impact on the risk-premium, contraryto the results of models where it is imposed exogenously.     

Real options maximizing survival probability under incomplete markets

By integrating the survival problem into the theory of real option valuation under incomplete markets, we analyze an entrepreneurial firm's optimal survival probability and the joint decisions of business investments and portfolio choices when the business investment opportunity has undiversifiable idiosyncratic risks. Based on the theory of stochastic control, we derive the semi-closed-form solutions for the firm's optimal survival probability, its investment thresholds and the implied option value. The results show that the goal of maximizing the survival probability greatly changes the entrepreneur's business investment strategies, the pattern of asset allocation and the correlation between the option value and the project risks. The comparative statics analysis shows that public authorities should subsidize entrepreneurs and maintain stabile financial markets in order to encourage entrepreneurship.     

Incomplete markets, labor supply and capital accumulation

Endogenous labor supply decisions are introduced in an equilibrium model of limited insurance against idiosyncratic shocks. Unlike in the standard case with exogenous labor (e.g. [Aiyagari, S.R., 1994. Uninsured idiosyncratic risk and aggregate saving. Quarterly Journal of Economics 109, 659-684; Huggett, M., 1997. The one-sector growth model with idiosyncratic shocks: steady states and dynamics. Journal of Monetary Economics 39, 385-403]), labor supply is likely to be lower than under complete markets. This is due to an ex post wealth effect on labor supply (rich productive agents work fewer hours) that runs counter the precautionary savings motive. As a result, equilibrium savings and output may be lower under incomplete markets. It is also found that long-run savings remain finite even when the interest rate equals the inverse of the discount factor.     

The Valuation of Assets under Moral Hazard

The design of managerial incentive contracts is examined in a setting in which economic agents are risk averse, and the actions of managers can affect asset returns which contain both systematic and idiosyncratic risks. It is shown that in the absence of moral hazard, owners of assets will insure managers against idiosyncratic risks, but with moral hazard, contracts will depend on both systematic and idiosyncratic risks. The traditional recommendation of asset pricing models, namely, to focus only on systematic risks, is thus proved to be valid only when there is no moral hazard. The major empirically testable predictions of the model are (1) managerial incentive contracts will generally depend on systematic as well as idiosyncratic risks, (2) idiosyncratic risks will generally be important in investment decisions, (3) the managers of firms with relatively high levels of idiosyncratic risks will have compensations that are less dependent on their firms' excess returns, and (4) the compensations of managers of larger firms will be relatively more dependent on the excess returns of their firms.     

Information Aggregation Bias and Samuelson's Dictum

Under the assumption of incomplete information, idiosyncratic shocks may not dissipate in the aggregate. An econometrician who incorrectly imposes complete information and applies the law of large numbers may be susceptible to information aggregation bias. Tests of aggregate economic theory will be misspecified even though tests of the same theory at the microlevel deliver the correct inference. A testable implication of information aggregation bias is “Samuelson's Dictum” or the idea that stock prices can simultaneously display “microefficiency” and “macroinefficiency;” an idea accredited to Paul Samuelson. Using firm-level data from the Center for Research in Security Prices, we present empirical evidence consistent with Samuelson's dictum. Specifically, we conduct two standard tests of the linear present value model of stock prices: a regression of future dividend changes on the dividend-price ratio and a test for excess volatility. We show that the dividend price ratio forecasts the future growth in dividends much more accurately at the firm level as predicted by the present value model, and that excess volatility can be rejected for most firms. When the same firms are aggregated into equal-weighted or cap-weighted portfolios, the estimated coefficients typically deviate from the present value model and “excess” volatility is observed; this is especially true for aggregates (e.g., S&P 500) that are used in most asset pricing studies. To investigate the source of our empirical findings, we propose a theory of aggregation bias based on incomplete information and segmented markets. Traders specializing in individual stocks conflate idiosyncratic and aggregate shocks to dividends. To an econometrician using aggregate data, these assumptions generate a rejection of the present value model even though individual traders are efficiently using their available information.     

Investment,consumption, and hedging under incomplete markets

Entrepreneurs often face undiversifiable idiosyncratic risks from their business investments. We extend the standard real options approach to an incomplete markets environment and analyze the joint decisions of business investments, consumption/savings, and portfolio selection. For a lump-sum investment payoff and an agent with a sufficiently strong precautionary savings motive, an increase in volatility can accelerate investment, contrary to the standard real options analysis. When the agent can trade the market portfolio to partially hedge against investment risk, the systematic volatility is compensated via the standard CAPM argument, and the idiosyncratic volatility generates a private equity premium. Finally, when the investment payoff is a series of flows, the agent's idiosyncratic risk exposure alters both the implied option value and the implied project value, causing a reversal of the results in the lump-sum payoff case.     

Revisiting the supply side effects of government spending

We revisit the macroeconomic effects of government consumption in the neoclassical growth model when agents face uninsured idiosyncratic investment risk. Under complete markets, a permanent increase in government consumption has no long-run effect on interest rates and capital intensity, while it increases work hours due to the negative wealth effect. These results are upset once we allow for incomplete markets. The same negative wealth effect now causes a reduction in risk taking and the demand for investment. This leads to a lower risk-free rate and, under certain conditions, also to a lower capital-labor ratio and lower productivity.     

Taxes, transfers and employment in an incomplete markets model

The consequences of increases in the scale of tax and transfer programs are assessed in the context of a model with idiosyncratic productivity shocks and incomplete markets. The effects are contrasted with those obtained in a stand-in household model featuring no idiosyncratic shocks and complete markets. The main finding is that the impact on hours remains very large, but the welfare consequences are very different. The analysis also suggests that tax and transfer policies have large effects on average labor productivity via selection effects on employment.     

The Effectiveness of Consumption Taxes and Transfers as Insurance Against Idiosyncratic Risk

We quantitatively evaluate the effectiveness of a consumption tax and lump-sum transfer program as insurance against idiosyncratic earnings risk. We use a heterogeneous agent, incomplete markets model in which households adjust savings and employment in each period in the presence of idiosyncratic productivity risk and a borrowing constraint. The model is calibrated to the U.S. economy. We find a weak insurance effect of the consumption tax and transfer program. Expanding the tax and transfer program from the current U.S. level increases the capital-output ratio and reduces the interest rate. Consumption inequality also decreases only slightly.     

Time-varying idiosyncratic risk and aggregate consumption dynamics

Long-term earnings losses for displaced workers are large and counter-cyclical. Similarly, the skewness of earnings growth rates is strongly pro-cyclical. This paper presents an incomplete markets business cycle model in which idiosyncratic risk varies over time in accordance with these empirical findings. These dynamics of idiosyncratic risk give rise to a cyclical precautionary savings motive that substantially raises the volatility of aggregate consumption growth. According to the model, idiosyncratic risk spiked during the Great Recession, leading to a substantial decline in aggregate consumption.     

Inattention, wealth inequality and equilibrium asset prices

Heterogeneity in planning propensity affects wealth inequality and asset prices. This paper presents an economy where attentive agents plan their consumption period by period, while inattentive agents plan every other period. Inattentive consumers face more uncertainty and trade at unfavorable prices. If the only source of uncertainty is future income, inattentive consumers accumulate more wealth. In contrast, with uncertain asset returns inattentive investors accumulate less wealth. Asset prices must induce attentive consumers to voluntarily bear the burden of adjusting to aggregate shocks and, as a result, are much more volatile than in a representative agent model with full attention.     

Optimal monetary policy in an economy with incomplete markets and idiosyncratic risk

This study investigates an incomplete markets economy in which the saving behavior of a continuum of infinitely lived agents is influenced by precautionary saving motives and borrowing constraints. Agents can use two types of assets (interest bearing IOUS and money) to smooth consumption. Money is valued because of a timing friction in the bond market. In particular, the bond market closes before agents observe their idiosyncratic productivity shock. I find that the Friedman rule is not optimal for this economy. The results indicate that the optimal allocation has a rate of inflation of 10%, and a positive amount of private credit held by the government. A positive inflation rate transfers resources from agents with big endowments to those holding bonds which improves risk sharing, and therefore, welfare. However, for higher rates of inflation, agents economize on money holdings, offsetting the insurance effects, and causing a reduction in welfare. Furthermore, higher rates of inflation discourage agents from borrowing, and the endogenous lower bound on bond holdings is higher than the exogenous borrowing limit. High rates of inflation, therefore, exacerbate frictions in the bond market.     

Complex Asset Markets

Investors' individual arbitrage models introduce idiosyncratic risk into complex asset strategies, driving up average returns and Sharpe ratios. However, despite the attractive risk-return trade-off, participation is limited. This is because effective Sharpe ratios in complex asset markets vary with investors' expertise. Investors with higher expertise, better models, and lower resulting idiosyncratic risk exposures realize higher Sharpe ratios. Their demand deters entry by less sophisticated investors. As predicted by our model, market dislocations are characterized by an increase in idiosyncratic risk, investor exit, and persistently elevated alphas and Sharpe ratios. The selection effect from higher expertise agents' more favorable Sharpe ratios is unique to our model and key to our main results.     

Idiosyncratic production risk, growth and the business cycle

We introduce a neoclassical growth economy with idiosyncratic production risk and incomplete markets. Each agent is an entrepreneur operating her own technology with her own capital stock. The general equilibrium is characterized by a closed-form recursion in the CARA-normal case. Incomplete markets introduce a risk premium on private equity, which reduces the demand for investment. As compared to complete markets, the steady state can thus have both a lower capital stock due to investment risk, and a lower interest rate due to precautionary savings. Furthermore, the anticipation of high real interest rates in the future feeds back into high risk premia and low investment in the present, thus slowing down convergence to the steady state. Our results highlight the importance of private risk premia for capital accumulation and business cycles.     

Uncertainty,Inflation, and Welfare

This paper studies the welfare costs and the redistributive effects of inflation in the presence of idiosyncratic liquidity risk, in a microfounded search‐theoretical monetary model. We calibrate the model to match the empirical aggregate money demand and the distribution of money holdings across households and study the effects of inflation under the implied degree of market incompleteness. We show that in the presence of imperfect insurance the estimated long‐run welfare costs of inflation are on average 40% to 55% smaller compared to a complete markets, representative agent economy, and that inflation induces important redistributive effects across households.     

A Rational Expectations Model of Financial Contagion

We develop a multiple asset rational expectations model of asset prices to explain financial market contagion. Although the model allows contagion through several channels, our focus is on contagion through cross-market rebalancing. Through this channel, investors transmit idiosyncratic shocks from one market to others by adjusting their portfolios' exposures to shared macroeconomic risks. The pattern and severity of financial contagion depends on markets' sensitivities to shared macroeconomic risk factors, and on the amount of information asymmetry in each market. The model can generate contagion in the absence of news, as well as between markets that do not directly share macroeconomic risks.     

Implied Risk Aversion Parameter from Option Prices

This paper estimates the representative investor's coefficient of relative risk aversion using option price data. Estimation is carried out using the method of simulated moments. Employing the following assumptions: a) agents have constant proportional risk averse preferences, b) complete markets exist, and c) asset returns are distributed lognormally, an objective function is constructed within the equivalent martingale measure framework. Unlike the case of equity markets, the implied risk aversion parameter from option prices is quite low and stays between zero and one.