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Modern portfolio theory suggests methods by which an investor can try and optimize his or her investment returns. It also helps in analyzing the risk factor associated with an asset. Concepts like Markowitz diversification, capital asset pricing model, efficient frontier, Capital market line, and Securities market line form an integral part of modern portfolio theory. According to this theory, returns offered by an asset is treated as a random variable.
In modern portfolio theory, A portfolio is treated as a weighted combination of assets that it comprises. Thus return of a portfolio is also calculated as a weighted combination of returns offered by all assets. Since return is treated as a random variable, expected value and variance of return can also be calculated. The standard deviation of return is taken to be a risk associated with a portfolio.
A portfolio is a collection of investments owned by an individual or financial institution. Holding a portfolio helps in reducing risk by process of diversification. A portfolio may comprise stocks, options, bonds, warrants, real estate, and even production facilities.
Modern portfolio theory assumes that investors do not like to invest in risky assets. This naturally suggests that given any two assets that offer equal, expected returns, an investor will opt for an asset that is less risky than others.
An important aspect of modern portfolio theory is diversification of assets included in a portfolio. A diversified portfolio reduces the risk of suffering from losses due to the materialization of risks associated with any single asset.
Plotting of all possible combination of assets in risk-return space reveals efficient frontier. The efficient frontier is a line that passes through the upper edge of a plotted region. Also called Markowitz frontier, it shows a portfolio that offers optimum possible returns.
Modern portfolio theory (MPT)—or portfolio theory—was introduced by Harry Markowitz with his paper “Portfolio Selection,” which appeared in the 1952 Journal of Finance. Thirty-eight years later, he shared a Nobel Prize with Merton Miller and William Sharpe for what has become a broad theory for portfolio selection.
Prior to Markowitz’s work, investors focused on assessing the risks and rewards of individual securities in constructing their portfolios. Standard investment advice was to identify those securities that offered the best opportunities for gain with the least risk and then construct a portfolio from these. Following this advice, an investor might conclude that railroad stocks all offered good risk-reward characteristics and compile a portfolio entirely from these. Intuitively, this would be foolish. Markowitz formalized this intuition. Detailing a mathematics of diversification, he proposed that investors focus on selecting portfolios based on those portfolios’ overall risk-reward characteristics instead of merely compiling portfolios from securities that each individually have attractive risk-reward characteristics. In a nutshell, inventors should select portfolios, not individual securities.
If we treat single-period returns for various securities as random variables, we can assign them expected values, standard deviations and correlations. Based on these, we can calculate the expected return and volatility of any portfolio constructed with those securities. We may treat volatility and expected return as proxy’s for risk and reward. Out of the entire universe of possible portfolios, certain ones will optimally balance risk and reward. These comprise what Markowitz called an efficient frontier of portfolios. An investor should select a portfolio that lies on the efficient frontier.
James Tobin (1958) expanded on Markowitz’s work by adding a risk-free asset to the analysis. This made it possible to leverage or deleverage portfolios on the efficient frontier. This lead to the notions of a super-efficient portfolio and the capital market line. Through leverage, portfolios on the capital market line are able to outperform portfolio on the efficient frontier.
Sharpe (1964) formalized the capital asset pricing model (CAPM). This makes strong assumptions that lead to interesting conclusions. Not only does the market portfolio sit on the efficient frontier, but it is actually Tobin’s super-efficient portfolio. According to CAPM, all investors should hold the market portfolio, leveraged or de-leveraged with positions in the risk-free asset. CAPM also introduced beta and relates an asset’s expected return to its beta.
Portfolio theory provides a context for understanding the interactions of systematic risk and reward. It has shaped how institutional portfolios are managed and motivated the use of passive investment techniques. The mathematics of portfolio theory is used in financial risk management and was a theoretical precursor for today’s value-at-risk measures.
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This glossary post was last updated: 29th December, 2021 | 0 Views.