Price Interpretability of Prediction Markets: A Convergence Analysis

TL;DR

This paper analyzes the convergence properties of prediction markets with risk-averse traders, introducing a unifying multivariate utility mechanism and deriving analytical results for limiting prices across various utility models.

Contribution

It proposes a novel multivariate utility-based mechanism that unifies existing market-making schemes and provides convergence analysis for diverse utility-based market models.

Findings

Limiting wealth distribution aligns with Pareto efficiency.

Limiting price converges to geometric mean in exponential utility markets.

Price can be characterized by systems of equations in CRRA utility markets.

Abstract

Prediction markets are long known for prediction accuracy. This study systematically explores the fundamental properties of prediction markets, addressing questions about their information aggregation process and the factors contributing to their remarkable efficacy. We propose a novel multivariate utility (MU) based mechanism that unifies several existing automated market-making schemes. Using this mechanism, we establish the convergence results for markets comprised of risk-averse traders who have heterogeneous beliefs and repeatedly interact with the market maker. We demonstrate that the resulting limiting wealth distribution aligns with the Pareto efficient frontier defined by the utilities of all market participants. With the help of this result, we establish analytical and numerical results for the limiting price in different market models. Specifically, we show that the limiting price converges to the geometric mean of agent beliefs in exponential utility-based markets. In risk-measure-based markets, we construct a family of risk measures that satisfy the convergence criteria and prove that the price can converge to a unique level represented by the weighted power mean of agent beliefs. In broader markets with Constant Relative Risk Aversion (CRRA) utilities, we reveal that the limiting price can be characterized by systems of equations that encapsulate agent beliefs, risk parameters, and wealth. Despite the potential impact of traders' trading sequences on the limiting price, we establish a price invariance result for markets with a large trader population. Using this result, we propose an efficient approximation scheme for the limiting price.