Abstract
Cooperative investment consists of two problems: finding an optimal cooperative investment strategy and fairly dividing investment outcome among participating agents. In general, the two problems cannot be solved separately. It is known that when agents’ preferences are represented by mean-deviation functionals, sharing of optimal portfolio creates instruments that, on the one hand, satisfy individual risk preferences but, on the other hand, are not replicable on an incomplete market, so that each agent is strictly better off in participating in cooperative investment than investing alone. This synergy effect is shown to hold when agents’ acceptance sets are represented by cash-invariant utility functions in the case of multiperiod investment with an arbitrary feasible investment set. In this case, a set of all Pareto-optimal allocations is characterized, and an equilibrium-based method for selecting a “fair” Pareto-optimal allocation is suggested. It is also shown that if exists, the “fair” allocation belongs to the core of the corresponding cooperative game. The equilibrium-based method is then extended to the case of arbitrary utility functions. The obtained results are demonstrated in a multiperiod cooperative investment problem with investors imposing drawdown constraints on investment strategies.
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Notes
In Wilson (1968), a group of agents participating in cooperative investment is called a syndicate.
Given two instruments with random payoffs \(X_1\) and \(X_2\), agent i prefers \(X_1\) if and only if \(U_i(X_1)>U_i(X_2)\).
For extension to the non-monotone case, see Acciaio (2007).
Mean-deviation functionals combine two quantities: expected value and general deviation measure of a random variable.
This is the so-called “common belief” assumption.
Two r.v.’s \(X:\Omega \rightarrow {\mathbb {R}}\) and \(Y:\Omega \rightarrow {\mathbb {R}}\) are said to be comonotone, if there exists a set \(A\subset \Omega \) such that \(P[A]=1\) and \((X(\omega _1)-X(\omega _2))(Y(\omega _1)-Y(\omega _2))\geqslant 0\) for all \(\omega _1, \omega _2 \in A\).
A probability space is atomless, if there exists an r.v. with continuous cumulative distribution function.
Namely, this holds if \(\Omega \) is atomless and \({\mathcal {L}}^2(\Omega )\) is separable.
Formally, we first introduce a probability measure \({\mathbb {P}}_{\mathcal {T}}\) on \({\mathcal {T}}\) such that \({\mathbb {P}}_{\mathcal {T}}(t_i)=1/k\), \(i=1,\ldots ,k\), if \({\mathcal {T}}=\{t_1,t_2,\ldots ,t_k=T\}\), and \({\mathbb {P}}_{\mathcal {T}}(S)=l(S)/T\) if \({\mathcal {T}}=[0,T]\), where S is any measurable subset of [0, T] with Lebesgue measure l(S), and then introduce a probability measure on \(\Omega \times {\mathcal {T}}\) as a produce measure of \({\mathbb {P}}\) and \({\mathbb {P}}_{\mathcal {T}}\).
See Theorem T25 in Chapter II in Dellacherie and Meyer (1978).
Filipovic and Kupper (2008) considered no optimal cooperative investment.
\(U_i\) has no local maxima if for all \(X\in {\mathcal {X}}\) and \(A\subset {\mathcal {X}}\) such that A is open and \(X\in A\), there exists \(X'\in A\) such that \(U_i(X')>U_i(X)\).
In fact, Theorem 1 in Dana et al. (1997) proves the existence of quasiequilibrium, i.e. a pair \((\mathbf{Z},P^*)\) such that (i) \(\mathbf{Z}\) is \(\mathbf{Q}\)-feasible, (ii) \(P^*(Z_i)=P^*(Q_i)\), \(i\in I\), and (iii) \(P^*(X)\geqslant P^*(Q_i)\), whenever \(U^*_i(X)>U^*_i(Z_i)\), \(i\in I\). A quasiequilibrium is a \(\mathbf{Q}\)-equilibrium if \(P^*(Z_i)>\inf \nolimits _{X\in {\mathcal {X}}_i}P^*(X)\), \(i\in I\).
(1) “invest,” “invest”; (2) “invest,” “not invest”; (3) “not invest,” “invest”; (4) “not invest,” “not invest”; (5) “invest,” and then if “win,” “invest” (if “lose,” “not invest”); and (6) “invest,” and then if “lose,” “invest” (if “win,” “not invest”).
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The authors are grateful to the referees for their comments and suggestions, which helped to improve the quality of the paper. The first author also thanks the University of Leicester for granting him the academic study leave to conduct this research.
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Grechuk, B., Zabarankin, M. Synergy effect of cooperative investment. Ann Oper Res 249, 409–431 (2017). https://doi.org/10.1007/s10479-015-2051-x
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DOI: https://doi.org/10.1007/s10479-015-2051-x