Sergio Ortobelli Lozza

Portfolio Selection Problems Consistent With Given Preference Orderings

This paper theoretically and empirically investigates the connection between portfolio theory and ordering theory. In particular, we examine three different portfolio problems and the respective orderings used to rank investors choices: (1) risk orderings, (2) variability orderings, and (3) tracking-error orderings. For each problem, we discuss the properties of the risk measures, variability measures, and tracking-error measures, as well as their consistency with investor choices. Finally, for each problem, we propose an empirical application of several admissible portfolio optimization problems using the US stock market. The proposed empirical analysis permits us to evaluate the ex-post impact of the optimal choices, thereby deriving completely different investors preference orderings during the recent financial crisis.

Diversification versus optimality: is there really a diversification puzzle?

ABSTRACT In this paper, we provide a general valuation of the diversification attitude of investors. First, we empirically examine the diversification of mean-variance optimal choices in the US stock market during the 11-year period 2003–2013. We then analyze the diversification problem from the perspective of risk-averse investors and risk-seeking investors. Second, we prove that investors’ optimal choices will be similar if their utility functions are not too distant, independent of their tolerance (or aversion) to risk. Finally, we discuss investors’ attitude towards diversification when the choices available to investors depend on several parameters.