A Theory of Portfolio Choice for Heterogeneous Investors

Li, Mingzhe (2025): A Theory of Portfolio Choice for Heterogeneous Investors.

Abstract

The Merton framework has difficulty explaining empirical phenomena in household finance and life-cycle patterns. This paper proposes a continuous-time heterogeneous agent model with common noise to study portfolio choice for heterogeneous investors. Households pay an "asset-exposure premium" (AEP) based on their wealth for bearing common financial risk. The AEP effect serves as a non-monotonic third term in optimal portfolio choice. For households near the borrowing constraint, the AEP effect is large and negative, overwhelming other motives and explaining limited participation. As wealth increases, the AEP effect turns positive before disappearing at high wealth, resulting in a hump-shaped profile of risky holdings. The AEP enables households to identify the risk characteristics of their portfolio, explaining why the low wealth exhibits underdiversification and why middle-to-high wealth households hold diversified portfolios. Furthermore, this paper introduces a steady state and solves the degeneration problem of the wealth distribution in the continuous-time ABH framework.

• Item Type: MPRA Paper
• Language: English
• Keywords: portfolio choice; household finance; limited participation; wealth distribution; heterogeneous agent; continuous time; underdiversification; life cycle
• Subjects: C - Mathematical and Quantitative Methods > C7 - Game Theory and Bargaining Theory > C73 - Stochastic and Dynamic Games ; Evolutionary Games ; Repeated Games; D - Microeconomics > D9 - Intertemporal Choice > D91 - Intertemporal Household Choice ; Life Cycle Models and Saving; E - Macroeconomics and Monetary Economics > E2 - Consumption, Saving, Production, Investment, Labor Markets, and Informal Economy > E21 - Consumption ; Saving ; Wealth; G - Financial Economics > G1 - General Financial Markets > G11 - Portfolio Choice ; Investment Decisions

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