OPTIMUM PORTFOLIO SELECTION

PORTFOLIO SELECTION

            The objective of every investor is to maximize his returns and minimize his risk. Diversification is the method adopted to reduce the risk. It essentially results in the construction of portfolios. The proper goal of construction of portfolios would be to generate a portfolio that provides the highest return and lowest risk. Such a portfolio would be an optimal portfolio. The process of finding the optimal portfolio is described as portfolio selection.

            The conceptual framework and analytical tools for determining the optimal portfolio in disciplined and objective manner have been provided by Harry Markowitz in his pioneering work on portfolio analysis described in his 1952 “JOURNAL OF FINANCE” article and subsequent book in 1959. His method of portfolio selection is come to be known as Markowitz model. In fact, Markowitz work marked the beginning of what is today the Modern Portfolio Theory.

FEASIBLE SET OF PORTFOLIOS

            With limited number of securities an investor can create a very large number of portfolios by combining these securities in different proportions. These constitute the feasible set of portfolios in which the investor can possibly invest. This is also known as the portfolio opportunity set.

            Each portfolio in the opportunity set is characterized by an expected return and a measure of risk, viz., and variance of the returns. Not every portfolio in the portfolio opportunity set is of interest to an investor. In an opportunity set some portfolios will be dominant over the others. A portfolio will dominate the other if it has either a lower variance and the same expected return as the other, or a higher return and the same variance as the other.  Portfolios that are dominated by the others are called as insufficient portfolios. An investor would not be interested in all the portfolios in the opportunity set. He would be interested only in the efficient portfolios.

EFFICIENT SET OF PORTFOLIOS

            To understand the concept of efficient portfolios, let us consider various combinations of securities and designate them as portfolios 1 to n. the expected returns of these portfolios may be worked out. The risk of these portfolios may be estimated by measuring the variance of the portfolio returns. The table below shows illustrative returns and variance of some portfolios:

Portfolio No.	Expected Return (per cent)	Variance (risk)
1	5.6	4.5
2	7.8	5.8
3	9.2	7.6
4	10.5	8.1
5	11.7	8.1
6	12.4	9.3
7	13.5	9.5
8	13.5	11.3
9	15.7	12.7
10	16.8	12.9

            If we compare portfolios 4 and 5, for the same variance of 8.1 portfolio no. 5 gives a higher expected return of 11.7, making it more efficient than portfolio no. 4. Again, if we compare portfolios 7 and 8 for the same expected return of 13.5%, the variance is lower for portfolio no.7, making it more efficient than portfolio no. 8. Thus the selection of the portfolios by the investor will be guided by two criteria:

• Given two portfolios with the same expected return, the investor will prefer the one with the lower risk.

• Given two portfolios with the same risk, the investor will prefer the one with the higher expected returns.

These criteria are based on the assumption that investors are rational and also risk averse. As they are rational they would prefer more returns to less returns. As they are risk averse, they would prefer less risk to more risk.

            The concept of efficient sets can be illustrated with the help of a graph. The expected returns and the variance can be depicted on a XY graph, measuring the expected returns on the Y-axis and the variance on the X-axis. The figure below depicts such a graph.

As a single point in the risk-return space would represent each possible portfolio in the opportunity set or the feasible set of portfolio enclosed within the two axes of the graph. The shaded area in the graph represents the set of all possible portfolios that can be constructed from a given set of securities. This opportunity set of portfolios takes a concave shape because it consists of portfolios containing securities that are less than perfectly correlated with each other.

Let us closely examine the diagram above. Consider portfolios F and E. Both the portfolios have the same expected return but portfolio E has less risk. Hence portfolio E would be preferred to portfolio F. Now consider portfolios C and E. Both have the same risk, but portfolio E offers more return for the same risk. Hence portfolio E would be preferred to portfolio C. Thus for any point in the risk-return space, an investor would like to move as far as possible in the direction of increasing returns and also as far as possible in the direction of decreasing risk. Effectively, he would be moving towards the left in search of decreasing risk and upwards in search of increasing returns.

Let us consider portfolios C and A. Portfolio C would be preferred to portfolio A because it offers less risk for the same level of return. In the opportunity set of portfolios represented in the diagram, portfolio C has the lowest risk compared to all other portfolios. Here portfolio C in this diagram represents the Global Minimum Variance Portfolio.

Comparing portfolios A and B, we find that portfolio B is preferable to portfolio A because it offers higher return for the same level of risk. In this diagram, point B represents the portfolio with the highest expected return among all the portfolios in the feasible set.

Thus we find that portfolios lying in the North West boundary of the shaded area are more efficient than all the portfolios in the interior of the shaded area. This boundary of the shaded area is called the Efficient Frontier because it contains all the efficient portfolios in the opportunity set. The set of portfolios lying between the global minimum variance portfolio and the maximum return portfolio on the efficient frontier represents the efficient set of portfolios. The efficient frontier is shown separately in Fig.

The efficient frontier is a concave curve in the risk-return space that extends from the minimum variance portfolio to the maximum return portfolio.

SELECTION OF OPTIMAL PORTFOLIO

The portfolio selection problem is really the process of delineating the efficient portfolios and then selecting the best portfolio from the set.

Rational investors will obviously prefer to invest in the efficient portfolios. The particular portfolio that an individual investor will select from the efficient frontier will depend on that investor's degree of aversion to risk. A highly risk averse investor will hold a portfolio on the lower left hand segment of the efficient frontier, while an investor who is not too risk averse will hold one on the upper portion of the efficient frontier.

The selection of the optimal portfolio thus depends on the investor's risk aversion, or conversely on his risk tolerance. This can be graphically represented through a series of risk return utility curves or indifference curves. The indifference curves of an investor are shown in Fig. Each curve represents different combinations of risk and return all of which are equally satisfactory to the concerned investor. The investor is indifferent between the successive points in the curve. Each successive curve moving upwards to the left represents a higher level of satisfaction or utility. The investor's goal would be to maximize his utility by moving up to the higher utility curve. The optimal portfolio for an investor would be the one at the point of tangency between the efficient frontier and his risk-return utility or indifference curve.

This is shown in Fig. The point O' represents the optimal portfolio. Markowitz used the technique of quadratic programming to identify the efficient portfolios. Using the expected return and risk of each security under consideration and the covariance estimates for each pair of securities, he calculated risk and return for all possible portfolios. Then, for any specific value of expected portfolio return, he determined the least risk portfolio using quadratic programming. With another value of expected portfolio return, a similar procedure again gives the minimum risk portfolio. The process is repeated with different values of expected return, the resulting minimum risk portfolios constitute the set of efficient portfolio