Lorenzo Garlappi

Keynes Meets Markowitz: The Trade-Off Between Familiarity and Diversification

We develop a model of portfolio choice to nest the views of Keynes, who advocates concentration in a few familiar assets, and Markowitz, who advocates diversification. We use the concepts of ambiguity and ambiguity aversion to formalize the idea of an investors “familiarity” toward assets. The model shows that for any given level of expected returns, the optimal portfolio depends on two quantities: relative ambiguity across assets and the standard deviation of the expected return estimate for each asset. If both quantities are low, then the optimal portfolio consists of a mix of familiar and unfamiliar assets; moreover, an increase in correlation between assets causes an investor to increase concentration in familiar assets (flight to familiarity). Alternatively, if both quantities are high, then the optimal portfolio contains only the familiar asset(s), as Keynes would have advocated. In the extreme case in which both quantities are very high, no risky asset is held (nonparticipation). This paper was accepted by Brad Barber, Teck Ho, and Terrance Odean, special issue editors.

Risk Premia and Preemption in R&D Ventures

I analyze the impact of competition on the risk premia of R&D ventures engaged in a multiple-stage patent race with technical and market uncertainty. After solving in closed form for the case of a two-stage race in continuous time, I show that a firms risk premium decreases as a consequence of technical progress and increases when a rival pulls ahead. Compared to the case where firms collude, R&D competition erodes the option value to mothball a project, reduces the completion time and the failure rate of R&D, and causes higher and more volatile risk premia. Numerical simulations reveal that competition can generate risk premia up to 500 annual basis points higher and up to three times more volatility than in a collusive industry.

Public Sector Science And The Strategy Of The Commons

We model the conditions under which incumbent firms may purposefully create an intellectual property (IP) commons such that no firm has the incentive to invest in new product development, despite the potential profitability of a public sector invention. The strategy of spoiling incentives to innovate by eliminating exclusive IP rights—the strategy of the commons—is motivated by a fear of cannibalization and supported by a credible threat. We show how the degree of potential cannibalization is related to this market failure and characterize the subgame perfect equilibrium in which the strategy of the commons is played. †We are grateful to Jim Brander, Iain Cockburn, Jerry Thursby, and participants of theNBERproductivityworkshop for thoughtful comments, and to the Social Sciences and Humanities Research Council of Canada (Grant No. 410-2004-1770) as well as the Mellon Foundation for generous financial support.

A State-Variable Decomposition Approach for Solving Portfolio Choice Problems

In this paper, we develop a new method for the solution of dynamic portfolio choice problems. Our approach consists of decomposing each state variable into a sum of its conditional mean and the corresponding zero-mean shock. Such a state variable decomposition (SVD) allows efficient computation of the conditional expectations required for the solution of the dynamic optimization problem. Under commonly used distributional assumptions for the state variable shocks (e.g., normality or lognormality), this decomposition allows closed-form evaluation of such expectations, thus avoiding computationally intensive quadrature or simulation-based techniques. Our approach can easily handle intermediate consumption, multiple risky assets, multiple state variables, portfolio constraints, non-expected utility preferences as well as portfolio problems in which wealth is not a redundant state variable. We illustrate the accuracy of the method by comparing our solution to either the analytical solution, whenever available, or the solution obtained by quadrature methods. Finally, we employ our method to solve a large-scale strategic asset allocation problem with recursive preferences and predictable asset returns similar to the one solved by Campbell, Chan, and Viceira (2003) via log-linear approximation. Our approach allows us to impose realistic no borrowing and short-selling constraints and its precision, unlike that of the log-linear approximation, does not rely on the elasticity of intertemporal substitution being close to unity. The versatility of our approach makes it a suitable solution method for a wide range of dynamic problems in finance and economics.

Can Investment Shocks Explain the Cross Section of Equity Returns

Using two macro-based measures and one return-based measure of investment-specific technology (IST) shocks, we find that over the 1964–2012 period, exposure to IST shocks cannot explain cross-sectional return spreads based on book-to-market, momentum, asset growth, net share issues, accrual, and price-to-earnings ratio. Only one of the two macro-based measures can explain a sizable portion of the value premium over the longer 1930–2012 period. We also find that the IST risk premium estimates are sensitive to the sample period, the data frequency, the test assets, and the econometric model specification. Impulse responses of aggregate investment and consumption indicate potential measurement problems in IST proxies, which may contribute to the sensitivity of IST risk premium estimates and the failure of IST shocks to explain cross-sectional returns. This paper was accepted by Neng Wang, finance.

Heterogeneous Innovation, Firm Creation and Destruction, and Asset Prices

We study the implications of creative destruction on asset prices. We develop a general equilibrium model of endogenous firm creation and destruction in which “incremental” innovation by incumbents and “radical” innovation by entrants drive productivity improvements. Firms’ incentives to innovate generate time-varying economic growth and countercyclical economic uncertainty. The model matches key properties of consumption and asset prices, as well as novel facts on the process of creative destruction in the United States obtained using a sample of patents from 1975–2013. We show that the interplay between incumbents and entrants is an important determinant of risks priced in the financial markets.Received June 2, 2014; accepted September 14, 2015 by Editor Wayne Ferson.

The Carry Trade and Uncovered Interest Parity When Markets Are Incomplete

Many of the leading models of the carry trade imply that, contrary to the empirical evidence, a countrys currency depreciates in times of high consumption and output growth, a manifestation of the Backus and Smith (1993) puzzle. We propose a modification of these models to account for financial market incompleteness and show that such a modification can induce positive correlation between currency appreciation and consumption or output growth while, at the same time, helping resolve the Backus and Smith (1993) and Brandt, Cochrane and SantaClara (2006) puzzles. Furthermore, in many of the existing models, the assumed fundamental cross-country differences (output volatility, growth, and risk attitude) responsible for interest rate differentials also appear at odds with the data. We document that default risk and financial openness are strongly related to interest rate differentials and carry trade profits in the data. The incomplete markets model we propose is consistent with these novel empirical facts.

Improving Performance By Constraining Portfolio Norms: A Generalized Approach to Portfolio Optimization

In this paper, we provide a general framework for determining the portfolio that has superior out-of-sample performance even in the presence of estimation error. This general framework relies on solving the traditional minimum-variance problem (based on the sample covariance matrix) but subject to the additional constraint that the norm of the portfolio weight vector must be smaller than a given threshold. We show that our general framework nests as special cases the shrinkage approaches of Jagannathan and Ma (2003) and Ledoit and Wolf (2004b), and the 1/N policy studied in DeMiguel, Garlappi, and Uppal (2007), and that all these policies can be interpreted as those of a Bayesian investor who has a certain prior belief on portfolio weights. We also use our general framework to propose several new portfolio strategies. Finally, we compare empirically (in terms of portfolio variance, Sharpe ratio, and turnover), the out-of-sample performance of the new polices we propose to ten strategies in the existing literature across ten datasets. We find that the new policies we propose can outperform the policies proposed in Jagannathan and Ma (2003) and Ledoit and Wolf (2004b), the 1/N policy evaluated in DeMiguel, Garlappi, and Uppal (2007), and also other strategies in the literature such as Brandt, Santa-Clara, and Valkanov (2005).

Risk Premia and Premption in R&D Ventures

I analyze the impact of competition on the risk premia of R&D ventures engaged in a multiple-stage patent race with technical and market uncertainty. After solving in closed-form for the case of a two-stage race in continuous-time, I show that a firms risk premium decreases as a consequence of technical progress and increases when a rival pulls ahead in the race. Compared to the case where firms collude, R&D competition (i) erodes the option value to mothball a project (ii) reduces the completion time and the failure rate of R&D and (iii) causes higher and more volatile in risk premia. Numerical simulations reveal that competition can generate risk premia up to 500 annual basis point higher and up to three times more volatile than in a collusive industry.