“Reverse-Engineering” the Market Portfolio

The market portfolio plays a pivotal role in asset pricing. W. Sharpe proposed a model for the market portfolio based on optimizing the excess expected returns to total risk. Unfortunately, empirical studies using Sharpe's model in the CAPM explain asset expected returns only to a moderate extent. The present study proposes a model for the market portfolio which maximally explains expected returns of assets, under a given asset pricing model. This model is compared with five other constructions, viz. the equally-weighted portfolio, the value-weighted portfolio, the maximum returns portfolio, the minimum risk portfolio, and the Sharpe portfolio, in terms of their risk-return properties, the statistical properties of their implied SMLs, and their efficiency.