Modern portfolio theory (MPT) refers to the theory of investment that seeks to maximize the expected return of portfolio at a given level of risk. Similarly it also attempts to diminish risk for a given level of return expected. To achieve this, portfolio manager choose the proportions of different assets in a portfolio carefully. The modern portfolio theory is extensively used for practice in the financial industry, however basic assumptions of this theory has faced certain challenges in fields like behavioral economics.
Modern Portfolio theory (MPT) presents the concept of diversification in investing by using mathematical formulation. It aims to select a collection of investment assets which has lower risk than any individual asset. It can be observed spontaneously as dynamic market conditions cause changes in value of different types of assets in conflicting ways. The prices in the bond market may fall independently from prices in the stocks market, thus there is overall lower risk in a collection of both bond and stocks assets as compared to individual asset. Moreover, the diversification reduces the risk even if cases where assets’ returns are positively correlated.
In technical terms, a Modern Portfolio theory (MPT) represents the return of asset as a normally distributed function or as an elliptically distributed random variable where risk is defined as the standard deviation of return. According to MPT, the return of a portfolio is equivalent to the weighted combination of the assets’ returns because the portfolio is modelled as a weighted combination of assets. MPT aims to reduce the total variance of the return of portfolio by combining various assets whose returns are negatively correlated or not positively correlated. MPT assumes that the markets are competent and investors are logical.
MPT stress the fact that assets in an investment portfolio must not be chosen individually where each asset is selected on the basis of its own merits. Instead, it is important to observe the changes in price of each asset relative to changes in the price of every other asset in the portfolio. Investing in the assets is basically the exchange between risk and expected return. The assets with higher expected returns are usually more risky.
MPT assists in the selection of a portfolio with the maximum possible expected return at a given level of risk. Similarly, MPT assists in the selection of a portfolio with the lowest possible risk at a given amount of expected return. Thus, it is not possible to have a targeted expected return exceeding the highest-returning available security except there is possibility of negative holdings. MPT stresses the diversification and assists the portfolio managers in finding the best possible diversification strategy.
A Portfolio Manager is responsible for building a portfolio of assets such as stocks, bonds and other assets that generates the maximum possible rate of return at the least possible level of risk. The portfolio management involves allocation of funds in various assets to achieve diversification of portfolio that offer maximum return at the lowest possible risk.