Optimal portfolio choice in the bond market

We consider the Merton problem of optimal portfolio choice when the traded instruments are the set of zero-coupon bonds. Working within a Markovian Heath–Jarrow–Morton model of the interest rate term structure driven by an infinite-dimensional Wiener process, we give sufficient conditions for the existence and uniqueness of an optimal trading strategy. When there is uniqueness, we provide a characterization of the optimal portfolio as a sum of mutual funds. Furthermore, we show that a Gauss–Markov random field model proposed by Kennedy [Math. Financ. 4, 247–258(1994)] can be treated in this framework, and explicitly calculate the optimal portfolio. We show that the optimal portfolio in this case can be identified with the discontinuities of a certain function of the market parameters.     

Optimal granularity for portfolio choice

Many optimization-based portfolio rules fail to beat the simple 1/N rule out-of-sample because of parameter uncertainty. In this paper we suggest a grouping strategy in which we first form groups of equally weighted stocks and then optimize over the resulting groups only. This strategy aims at balancing the trade-off between the benefits from optimization and the losses from estimation risk. We rely on Monte-Carlo simulations to illustrate the performance of the strategy, and we derive the optimal group size for a simplified setup. Furthermore, we show that estimation risk also has an impact via the criterion by which the assets are sorted into groups (like the expected excess returns or betas), but does not negate the grouping approach. We relate our work to linear asset pricing models, and we conduct out of sample back-tests in order to confirm the validity of our grouping strategy empirically.     

Optimal portfolio choice and the valuation of illiquid securities

Traditional models of portfolio choice assume that investorscan continuously trade unlimited amounts of securities. In reality,investors face liquidity constraints. I analyze a model whereinvestors are restricted to trading strategies that are of boundedvariation. An investor facing this type of illiquidity behavesvery differently from an unconstrained investor. A liquidity-constrainedinvestor endogenously acts as if facing borrowing and short-sellingconstraints, and one may take riskier positions than in liquidmarkets. I solve for the shadow cost of illiquidity and showthat large price discounts can be sustained in a rational model.     

Are TIPS the “real” deal?: A conditional assessment of their role in a nominal portfolio

This paper documents predictable time-variation in the real return beta of US Treasury Inflation Protected Securities (TIPS) and in the Sharpe ratios of both indexed and conventional bonds. The conditional mean and volatility of both bonds and their conditional correlation first are estimated from predetermined variables. These estimates then are used to compute conditional real return betas and Sharpe ratios. The time-variation in real return betas and the correlation between TIPS and nominal bonds coincides with major developments in the fixed-income market. One implication of this predictability is that portfolio managers can assess more efficiently the risk of investing in TIPS versus conventional bonds. Conditional Sharpe ratios indicate that over the sample period, TIPS had superior volatility-adjusted returns relative to nominal bonds. This finding is striking in view of the absence of a major inflation scare during the sample period from February 1997 through August 2001, but is loosely consistent with the possibility that TIPS elevated rather than reduced Treasury borrowing costs. On the other hand, mean–variance spanning tests indicate that TIPS did not enhance the mean–variance efficiency of diversified portfolios.     

Optimal portfolio choice for a behavioural investor in continuous-time markets

The aim of this work consists in the study of the optimal investment strategy for a behavioural investor, whose preference towards risk is described by both a probability distortion and an S-shaped utility function. Within a continuous-time financial market framework and assuming that asset prices are modelled by semimartingales, we derive sufficient and necessary conditions for the well-posedness of the optimisation problem in the case of piecewise-power probability distortion and utility functions. Finally, under straightforwardly verifiable conditions, we further demonstrate the existence of an optimal strategy.     

Optimal portfolio choice for investors with industry-specific labor income risks

We study optimal investment decisions for long-horizon investors with industry-specific labor income risks. We find that in addition to the volatility of labor income growth, the correlation between labor income and risky asset returns is another important factor that affects the optimal portfolio decisions and may provide a plausible explanation for the mixed empirical evidence of the relationship between labor income risk and portfolio holdings. Depending on its relative covariance with stock and bond returns, labor income may help resolve or deepen the asset allocation puzzle.     

Optimal portfolio choice of gold assets in the differential market and differential game structures

Portfolio choices of gold-related assets for market investors and dealers may not only depend on price differences and the inflation rate, but may also react to the market participants’ strategic behavior and risk attitude. This study develops a two-agent stochastic differential game model to solve the portfolio choice problem of the asset allocations of gold spot, futures, and cash for market participators who are exposed to inflation risks. The equilibrium prices of spot and futures driven by the volatility rate and co-variances that reflect various risk sources are also determined. Specifically, regarding the choice of hedging tools, market participators may prefer gold spot to futures for the purpose of hedging inflation risk. By capturing the stylistic facts of differential market and multiple agent structures, the article can develop a more reasonable and practical model to usefully explain the gold portfolio choices and pricing in the gold markets.     

Algorithmic portfolio choice: lessons from panel survey data

Automated asset management offerings algorithmically assign risky portfolios to individual investors based on investor characteristics such as age, net income, or self-assessment of risk aversion. Using new German household panel data, we investigate the key household characteristics that drive private asset allocation decisions. This information allows us to assess which set of variables should be included in algorithmic portfolio advice. Using heavily cross-validated classification trees, we find that a combination of household balance sheet variables—describing the ability to take risks (e.g., net wealth)—and household personal characteristics—describing the willingness to take risks (e.g., risk aversion)—best explain the cross-sectional variation in household portfolio choice. Our empirical evidence is in line with models of portfolio choice under decreasing relative risk aversion and fixed investment costs. The results suggest the utility of a more holistic modeling of household characteristics. Including background risks in the form of household leverage not only makes investment sense, but is also the new regulatory reality under MIFID II rules. Robo-advisors are strongly advised to act accordingly.     

Liquidity and conditional portfolio choice: A nonparametric investigation

This paper studies the relation between liquidity and optimal portfolio allocations. Given that the portfolio problem of a constant relative risk aversion investor does not have a closed-form solution, we use a nonparametric approach to estimate the optimal allocations. Using a sample of NYSE stocks from 1963–2000, we find that the optimal portfolio weight in small stocks is strongly increasing in liquidity at short daily and weekly horizons. This result is consistent for three different measures of liquidity: price impact, dollar volume, and turnover. However, liquidity does not influence the optimal portfolio choice for large stocks, nor for longer monthly investment horizons.     

Strategy as a portfolio of real options

In financial terms, a business strategy is much more like a series of options than like a single projected cash flow. Executing a strategy almost always involves making a sequence of major decisions. Some actions are taken immediately while others are deliberately deferred so that managers can optimize their choices as circumstances evolve. While executives readily grasp the analogy between strategy and real options, until recently the mechanics of option pricing was so complex that few companies found it practical to use when formulating strategy. But advances in both computing power and our understanding of option pricing over the last 20 years now make it feasible to apply real-options thinking to strategic decision making. To analyze a strategy as a portfolio of related real options, this article exploits a framework presented by the author in "Investment Opportunities as Real Options: Getting Started on the Numbers" (HBR July-August 1998). That article explained how to get from discounted-cash-flow value to option value for a typical project; in other words, it was about reaching a number. This article extends that framework, exploring how, once you've worked out the numbers, you can use option pricing to improve decision making about the sequence and timing of a portfolio of strategic investments. Timothy Luehrman shows executives how to plot their strategies in two-dimensional "option space," giving them a way to "draw" a strategy in terms that are neither wholly strategic nor wholly financial, but some of both. Such pictures inject financial discipline and new insight into how a company's future opportunities can be actively cultivated and harvested.     

Exploring the benefits of using stock characteristics in optimal portfolio strategies

I examine the benefits of using stock characteristics to model optimal portfolio weights in stock selection strategies using the characteristic portfolio approach of Brandt, Santa-Clara, and Valkanov. [2009. “Parametric Portfolio Policies: Exploiting Characteristics in the Cross-section of Equity Returns.” Review of Financial Studies 22: 3411–3447]. I find that there are significant out-of-sample performance benefits in using characteristics in stock selection strategies even after adjusting for trading costs, when investors can invest in the largest 350 UK stocks. Imposing short selling restrictions on the characteristic portfolio strategy leads to more consistent performance. The performance benefits are concentrated in the earlier part of the sample period and have disappeared in recent years. I find that there no performance benefits in using stock characteristics when using random subsets of the largest 350 stocks.     

Exploring the benefits of international government bond portfolio diversification strategies

We use the Bayesian approach of Wang (1998) to examine the diversification benefits of investing in international government bonds. We find that no short-selling constraints substantially reduce but do not eliminate the diversification benefits when only investing in G7 government bonds with different maturities. There are significant diversification benefits when using the G7 bonds, an inflation-linked bond index, and emerging market bonds even in the presence of no short-selling constraints. The superior performance is driven by the emerging markets bonds. We also find that the diversification benefits vary across different economic states.     

Optimal portfolio selection in nonlinear arbitrage spreads

This paper analytically solves the portfolio optimization problem of an investor faced with a risky arbitrage opportunity (e.g. relative mispricing in equity pairs). Unlike the extant literature, which typically models mispricings through the Ornstein–Uhlenbeck (OU) process, we introduce a nonlinear generalization of OU which jointly captures several important risk factors inherent in arbitrage trading. While these factors are absent from the standard OU, we show that considering them yields several new insights into the behavior of rational arbitrageurs: Firstly, arbitrageurs recognizing these risk factors exhibit a diminishing propensity to exploit large mispricings. Secondly, optimal investment behavior in light of these risk factors precipitates the gradual unwinding of losing trades far sooner than is entailed in existing approaches including OU. Finally, an empirical application to daily FTSE100 pairs data shows that incorporating these risks renders our model's risk-management capabilities superior to both OU and a simple threshold strategy popular in the literature. These observations are useful in understanding the role of arbitrageurs in enforcing price efficiency.     

International portfolio diversification benefits: Cross-country evidence from a local perspective

We investigate how the benefits of international portfolio diversification differ across countries from the perspective of a local investor. We find that the benefits of investing abroad are largest for investors in developing countries, including when controlling for currency effects. Most of the benefits are obtained from investing outside the region of the home country. These global diversification benefits remain large when controlling for short-sales constraints in developing stock markets. The gains from international portfolio diversification appear to be largest for countries with high country risk. In addition to this cross-sectional evidence, we also provide evidence that diversification benefits vary over time as country risk changes. We find that diversification benefits have decreased for most countries in our sample over the past two decades.     

The next big thing in health benefits: consumer choice

Consumers are the only ones who can affect all decision points that drive health care cost and quality. As a result, consumers' health and financial security depend on their taking more responsibility for their health care decisions and having the tools and information needed to do so successfully. This article explains the five key decision points that drive health care cost and quality, how technology aids marketplace innovations, and how employers can help advance consumer choice in order to push the health care system to deliver better care and keep inflation in check.     

Labor income dynamics at business-cycle frequencies: Implications for portfolio choice

Young agents with low wealth-income ratios counter factually hold more stock than young, rich agents and old agents using the standard portfolio choice model with i.i.d. stock returns and labor income. This paper matches the countercyclical volatility and procyclical mean of U.S. labor income and finds that, consistent with U.S. data, young, poor agents now hold less stock than both young, rich agents and old agents, and no stock a large fraction of the time. Our results suggest that the predictability of labor income growth at a business-cycle frequency, particularly the countercyclical variation in volatility, plays an important role in a young agent's decision making about her portfolio's stock holding.     

Measuring portfolio credit risk correctly: Why parameter uncertainty matters

Why should risk management systems account for parameter uncertainty? In addressing this question, the paper lets an investor in a credit portfolio face non-diversifiable uncertainty about two risk parameters – probability of default and asset-return correlation – and calibrates this uncertainty to a lower bound on estimation noise. In this context, a Bayesian inference procedure is essential for deriving and analyzing the main result, i.e. that parameter uncertainty raises substantially the tail risk perceived by the investor. Since a measure of tail risk that incorporates parameter uncertainty is computationally demanding, the paper also derives a closed-form approximation to such a measure.     

Entrepreneurship and household portfolio choice: Evidence from the China Household Finance Survey

The efficient allocation of household assets is important for household wealth and entrepreneurial activities. However, there is scarce evidence on how entrepreneurial activities influence household financial decisions. We use a simple model to characterize the impact of entrepreneurship on household portfolio choice and the two underlying channels—the diversification effect and the risk substitution effect. We also empirically examine the impact of entrepreneurship using data from the 2013, 2015, and 2017 waves of the China Household Finance Survey (CHFS). The empirical results show that entrepreneurship significantly decreases both household risky market participation and risky asset holding. These findings are robust to alternative measurements of key variables, different model specifications, and Lewbel’s two-stage estimators. This study also verifies the co-existence of both the diversification and risk substitution effects. In particular, the net effect of entrepreneurship on household portfolio choice varies between urban and rural areas due to the different offsetting results between the two effects.     

Robust multivariate portfolio choice with stochastic covariance in the presence of ambiguity

This paper provides the optimal multivariate intertemporal portfolio for an ambiguity averse investor, who has access to stocks and derivative markets, in closed form. The stock prices follow stochastic covariance processes and the investor can have different levels of uncertainty about the diffusion parts of the stocks and the covariance structure. We find strong evidence that the optimal exposures to stock and covariance risks are significantly affected by ambiguity aversion. Welfare analyses show that investors who ignore model uncertainty incur large losses, larger than those suffered under the embedded one-dimensional cases. We further confirm large welfare losses from not trading in derivatives as well as ignoring intertemporal hedging, we study the impact of ambiguity in that regard and justify the importance of including these factors in the scope of portfolio optimization. Conditions are provided for a well-behaved solution in general, together with verification theorems for the incomplete market case.     

On the robustness of international portfolio diversification benefits to regime-switching volatility

We examine if the benefits of international portfolio diversification are robust to time-varying asset return volatility. Since diversified portfolios are subject to common cross-country shocks, we focus on the transmission mechanism of such shocks in the presence of regime-switching volatility. Generally, market linkages are stable with little evidence of increased market interdependence in turbulent periods. Furthermore, risk reduction is consistently delivered for the US investor who holds foreign equity.