Mean-semivariance behavior: An alternative behavioral model

The most widely-used measure of an asset's risk, beta, stems from an equilibrium in which investors display mean-variance behavior. This behavioral criterion assumes that portfolio risk is measured by the variance (or standard deviation) of returns, which is a questionable measure of risk. The semivariance of returns is a more plausible measure of risk (as Markowitz himself admits) and is backed by theoretical, empirical, and practical considerations. It can also be used to implement an alternative behavioral criterion, mean-semivariance behavior, that is almost perfectly correlated to both expected utility and the utility of mean compound return.downside risk; semideviation; asset pricing;

p-probabilistic k-anonymous microaggregation for the anonymization of surveys with uncertain participation

We develop a probabilistic variant of k-anonymous microaggregation which we term p-probabilistic resorting to a statistical model of respondent participation in order to aggregate quasi-identifiers in such a manner that k-anonymity is concordantly enforced with a parametric probabilistic guarantee. Succinctly owing the possibility that some respondents may not finally participate, sufficiently larger cells are created striving to satisfy k-anonymity with probability at least p. The microaggregation function is designed before the respondents submit their confidential data. More precisely, a specification of the function is sent to them which they may verify and apply to their quasi-identifying demographic variables prior to submitting the microaggregated data along with the confidential attributes to an authorized repository. We propose a number of metrics to assess the performance of our probabilistic approach in terms of anonymity and distortion which we proceed to investigate theoretically in depth and empirically with synthetic and standardized data. We stress that in addition to constituting a functional extension of traditional microaggregation, thereby broadening its applicability to the anonymization of statistical databases in a wide variety of contexts, the relaxation of trust assumptions is arguably expected to have a considerable impact on user acceptance and ultimately on data utility through mere availability.Peer ReviewedPostprint (author's final draft

Spurious Welfare Reversals in International Business Cycle Models

Several papers on international business cycles have documented spurious welfare reversals, in that incomplete market economies can produce higher welfare than the complete market economy. This paper demonstrates how conventional linearization, as used in King, Plosser, and Rebelo (1988), can generate approximation errors that are large enough to result in such reversals. Using a two-country production economy without capital, we argue that spurious welfare reversals are not only possible but also plausible under reasonable parameter values. As a constructive alternative, this paper proposes an approximation method that modifies the conventional linearization method by a bias correction---the linear approximation around a 'stochastic' steady state. We show that this method can be easily implemented to accurately approximate the exact solution and therefore produce the correct welfare ordering. The accuracy of the proposed method is far better than that of the conventional linearization method and as good as that of a method involving a second-order expansion.Linearization, Stochastic steady state, Welfare, Risk sharing

Aspects of Investor Behavior Under Risk

The three sections of this paper support three related conclusions. First, asset demands with the familiar properties of wealth homogeneity and linearity in expected returns follow as close approximations from expected utility maximizing behavior under the assumptions of constant relative risk aversion and joint normally distributed asset returns. Second, although such asset demands exhibit a symmetric coefficient matrix with respect to the relevant vector of expected asset returns, symmetry is not a general property, and the available empirical evidence warrants rejecting it for both institutional and individual investors in the United States. Finally, in a manner analogous to the finite maximum exhibited by quadratic utility, a broad class of mean-variance utility functions also exhibits a form of wealth satiation which necessarily restricts it range of applicability.

On efficiency of mean-variance based portfolio selection in DC pension schemes

We consider the portfolio selection problem in the accumulation phase of a defined contribution (DC) pension scheme. We solve the mean-variance portfolio selection problem using the embedding technique pioneered by Zhou and Li (2000) and show that it is equivalent to a target-based optimization problem, consisting in the minimization of a quadratic loss function. We support the use of the target-based approach in DC pension funds for three reasons. Firstly, it transforms the difficult problem of selecting the individual's risk aversion coefficient into the easiest task of choosing an appropriate target. Secondly, it is intuitive, flexible and adaptable to the member's needs and preferences. Thirdly, it produces final portfolios that are efficient in the mean-variance setting. We address the issue of comparison between an efficient portfolio and a portfolio that is optimal according to the more general criterion of maximization of expected utility (EU). The two natural notions of Variance Inefficiency and Mean Inefficiency are introduced, which measure the distance of an optimal inefficient portfolio from an efficient one, focusing on their variance and on their expected value, respectively. As a particular case, we investigate the quite popular classes of CARA and CRRA utility functions. In these cases, we prove the intuitive but not trivial results that the mean-variance inefficiency decreases with the risk aversion of the individual and increases with the time horizon and the Sharpe ratio of the risky asset. Numerical investigations stress the impact of the time horizon on the extent of mean-variance inefficiency of CARA and CRRA utility functions. While at instantaneous level EU-optimality and efficiency coincide (see Merton (1971)), we find that for short durations they do not differ significantly. However, for longer durations - that are typical in pension funds - the extent of inefficiency turns out to be remarkable and should be taken into account by pension fund investment managers seeking appropriate rules for portfolio selection. Indeed, this result is a further element that supports the use of the target-based approach in DC pension schemes.Mean-variance approach; efficient frontier; expected utility maximization; defined contribution pension scheme; portfolio selection; risk aversion; Sharpe ratio

Expert Opinions and Logarithmic Utility Maximization in a Market with Gaussian Drift

This paper investigates optimal portfolio strategies in a financial market where the drift of the stock returns is driven by an unobserved Gaussian mean reverting process. Information on this process is obtained from observing stock returns and expert opinions. The latter provide at discrete time points an unbiased estimate of the current state of the drift. Nevertheless, the drift can only be observed partially and the best estimate is given by the conditional expectation given the available information, i.e., by the filter. We provide the filter equations in the model with expert opinion and derive in detail properties of the conditional variance. For an investor who maximizes expected logarithmic utility of his portfolio, we derive the optimal strategy explicitly in different settings for the available information. The optimal expected utility, the value function of the control problem, depends on the conditional variance. The bounds and asymptotic results for the conditional variances are used to derive bounds and asymptotic properties for the value functions. The results are illustrated with numerical examples.Comment: 21 page

Intertemporal Asset Pricing Without Consumption Data

This paper proposes a new way to generalize the insights of static asset pricing theory to a multi-period setting. The paper uses a loglinear approximation to the budget constraint to substitute out consumption from a standard intertemporal asset pricing model. In a homoskedastic lognormal selling, the consumption-wealth ratio is shown to depend on the elasticity of intertemporal substitution in consumption, while asset risk premia are determined by the coefficient of relative risk aversion. Risk premia are related to the covariances of asset returns with the market return and with news about the discounted value of all future market returns.