Counter-monotonic risk allocations and distortion risk measures

TL;DR

This paper investigates the structure of Pareto-optimal risk allocations under counter-monotonicity constraints in markets with agents exhibiting various risk preferences, using distortion risk measures and applying results to portfolio management.

Contribution

It provides a systematic analysis of counter-monotonic risk sharing with distortion risk measures across different risk preference settings, including explicit characterizations and portfolio strategies.

Findings

Counter-monotonic allocations arise with risk-seeking agents.

Explicit optimal strategies are derived for portfolio management.

Risk-seeking agents lead to more risky investments.

Abstract

In risk-sharing markets with aggregate uncertainty, characterizing Pareto-optimal allocations when agents might not be risk averse is a challenging task, and the literature has only provided limited explicit results thus far. In particular, Pareto optima in such a setting may not necessarily be comonotonic, in contrast to the case of risk-averse agents. In fact, when market participants are risk-seeking, Pareto-optimal allocations are counter-monotonic. Counter-monotonicity of Pareto optima also arises in some situations for quantile-optimizing agents. In this paper, we provide a systematic study of efficient risk sharing in markets where allocations are constrained to be counter-monotonic. The preferences of the agents are modelled by a common distortion risk measure, or equivalently, by a common Yaari dual utility. We consider three different settings: risk-averse agents, risk-seeking agents, and those with an inverse S-shaped distortion function. In each case, we provide useful characterizations of optimal allocations, for both the counter-monotonic market and the unconstrained market. To illustrate our results, we consider an application to a portfolio choice problem for a portfolio manager tasked with managing the investments of a group of clients, with varying levels of risk aversion or risk seeking. We determine explicitly the optimal investment strategies in this case. Our results confirm the intuition that a manager investing on behalf of risk-seeking agents tends to invest more in risky assets than a manager acting on behalf of risk-averse agents.