Portfolio Theory: N-Asset Portfolios & Diversification

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Questions and Answers

What is the primary goal of portfolio diversification?

  • To maximize returns regardless of risk.
  • To spread risk by constructing portfolios with a large number of securities. (correct)
  • To eliminate all risk from a portfolio.
  • To construct portfolios with a small number of securities to concentrate gains.

What characterizes the efficient frontier?

  • The set of portfolios that offer the lowest possible return for a given level of risk.
  • The set of portfolios with the highest risk.
  • The set of portfolios that offers the highest expected return for a given level of risk. (correct)
  • The set of portfolios that are impossible to achieve.

What is the effect of increasing the number of assets in a portfolio on diversifiable risk?

  • Diversifiable risk initially decreases but then increases after a certain number of assets.
  • Diversifiable risk decreases, approaching zero as the number of assets increases. (correct)
  • Diversifiable risk increases linearly with the number of assets.
  • Diversifiable risk remains constant regardless of the number of assets.

What is the impact of individual asset risk in a well-diversified portfolio?

<p>Individual risk matters less, and the portfolio risk is mainly determined by the covariances between assets. (C)</p>
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Which of the following is an accurate description of diversification?

<p>Investing in a portfolio with a large number of securities whose returns are not heavily positively correlated. (A)</p>
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What is the key characteristic of an efficient portfolio?

<p>It has lower variance or higher expected return compared to other portfolios. (C)</p>
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What is the shape of the efficient frontier when plotted with expected return on the y-axis and standard deviation on the x-axis if short-selling and riskless lending/borrowing are not allowed?

<p>A hyperbola. (B)</p>
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What is the shape of the efficient frontier when plotted with expected return on the y-axis and standard deviation on the x-axis if short-selling is allowed, but riskless lending/borrowing is not?

<p>An unconstrained hyperbola. (A)</p>
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What is the shape of the efficient frontier when plotted with expected return on the y-axis and standard deviation on the x-axis if both short-selling and riskless lending/borrowing are allowed?

<p>A straight line. (C)</p>
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In the context of portfolio theory, what does 'short-selling' refer to?

<p>Selling an asset that the investor does not own. (C)</p>
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How does precluding short-selling affect the constraints in portfolio optimization?

<p>It imposes additional constraints, such as individual asset allocations being between 0 and 1. (B)</p>
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What is a riskless asset in the context of portfolio theory?

<p>An asset with a fixed return over a given period and zero risk. (B)</p>
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What does riskless lending refer to?

<p>Lending to an entity (like a treasury) at a fixed interest rate. (C)</p>
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What characterizes riskless borrowing?

<p>Taking out a loan at a fixed interest rate. (C)</p>
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In a portfolio consisting of a risky asset and a risk-free asset, how is the portfolio's risk level determined?

<p>The portfolio’s risk is proportional to the allocation in the risky asset. (D)</p>
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What is the tangency portfolio?

<p>The portfolio of risky securities where a line from the risk-free rate is tangent to the efficient frontier. (A)</p>
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Which of the following best describes the One-Fund Theorem?

<p>A single fund of assets, combined with lending or borrowing at the risk-free rate, can create efficient portfolios for all investors. (A)</p>
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In Modern Portfolio Theory (MPT), what is the primary role of utility theory?

<p>To identify the optimal portfolio for a specific investor based on their risk preferences. (A)</p>
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What are the key assumptions of Modern Portfolio Theory (MPT)?

<p>Single-period investment horizons, and investors focus only on mean and variance of returns. (C)</p>
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According to Modern Portfolio Theory (MPT), how do investors make portfolio choices?

<p>Investors choose portfolios based on expected return and variance of return. (B)</p>
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What condition makes the mean-variance approach optimal within utility theory?

<p>When investors have quadratic utility functions or returns are normally distributed. (C)</p>
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What does variance measure in the context of portfolio theory?

<p>The dispersion or spread of possible returns around the expected return. (B)</p>
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What do indifference curves represent in the context of investor preferences?

<p>The set of portfolios that provide the same level of expected utility to an investor. (A)</p>
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If Investor X's indifference curves are steeper than Investor Y's, what does this imply?

<p>Investor X is more risk-averse than Investor Y. (C)</p>
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What does covariance measure between two assets in a portfolio?

<p>The degree to which the returns of two assets move together. (A)</p>
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How does the correlation between assets affect portfolio risk?

<p>Higher positive correlation increases portfolio risk, while negative or low correlation reduces it. (D)</p>
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Suppose a portfolio consists of 20% stock A and 80% stock B. If stock A returns 10% and stock B returns 5%, what is the portfolio return, assuming no other external factors?

<p>0.06 (B)</p>
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Consider a 2-asset portfolio. Which of the following statements is true regarding the impact of correlation on the expected return and variance?

<p>Correlation affects the variance but not the expected return. (D)</p>
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If two securities are perfectly positively correlated ($\rho = 1$), what is the implication for portfolio risk?

<p>Portfolio risk is maximized; diversification provides no benefit. (A)</p>
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If two securities are perfectly uncorrelated ($\rho = 0$), how is the portfolio variance calculated?

<p>Portfolio variance is the sum of the weighted variances of each asset. (A)</p>
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If two securities are perfectly negatively correlated ($\rho = -1$), what is a key benefit for constructing a portfolio with these assets?

<p>The portfolio risk can be completely eliminated under certain asset allocations.. (A)</p>
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An investor owns £200 of stock A and £800 of stock B. Another investor owns £2000 of stock A and £8000 of stock B. Assuming no shorting, is there any difference between their portfolios?

<p>No, because both portfolios are comprised of the same percentage allocations to Stock A and Stock B (A)</p>
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What are the two specification choices that are required to implement Modern Portfolio Theory (MPT)?

<p>Specify the opportunity set and determine the efficient portfolio with an ideal asset allocation (A)</p>
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Which of the following would be considered a practical method for diversifying an investment stock portfolio?

<p>Buy stocks from different countries and sectors (A)</p>
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An investor selects their portfolio based on reward and risk characteristics. What types of function would be optimal?

<p>Quadratic utility function and single period horizon returns (C)</p>
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Flashcards

Portfolio Diversification

Spreading investments across various securities to reduce risk.

Efficient Portfolio

A portfolio where no other portfolio offers less variance and higher expected return.

Efficient Frontier

Graph of the set of efficient portfolios.

Short Selling

Selling an asset that you do not own.

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Riskless Lending and Borrowing

Borrowing and lending at a fixed interest rate

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Tangency Portfolio

Portfolio of risky securities tangent to the efficient frontier.

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One-Fund Theorem

Combining a tangency portfolio and a risk-free asset to create efficient portfolios.

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Investment Portfolio

A collection of securities and their components invested in a security.

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Modern Portfolio Goal

Specify investment universe and estimate assets risk characteristics.

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Risk Aversion

Investors demand higher reward for taking higher risk.

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Indifference Curve

A constant expected utility.

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Covariance

How assets move together.

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Portfolio correlations

Correlation reduces portfolio risk.

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Study Notes

  • Portfolio theory focuses on constructing portfolios with multiple securities to mitigate risk through diversification

N-Asset Portfolio Basics

  • A portfolio consists of N securities, where N is greater than or equal to 2
  • Rp represents the return of the portfolio
  • μp signifies the expected return of the portfolio
  • σp² denotes the variance of the portfolio

Diversification Explained

  • Diversification involves spreading investments across a large number of securities to reduce risk
  • This is achieved by investing equally in N securities
  • On average, securities usually have a positive correlation
  • Average variance is greater than average covariance

Portfolio Diversification Definition

  • Investing in a portfolio with numerous securities reduces portfolio risk

Efficient Frontier

  • An efficient portfolio means an investor cannot find another portfolio with less variance or higher expected returns
  • The efficient frontier consists of the set of efficient portfolios

Key Observations with N Securities

  • There exists a global minimum risk portfolio G
  • There is a global maximum expected return asset M1
  • There is a global minimum expected return asset M2

MPT Assumptions

  • A single-period investment time horizon is present
  • Asset risk is assessed using the mean and variance only
  • Investors prefer non-satiation
  • Investors are risk-averse

Practical Diversification Strategies

  • Purchasing stocks from various countries
  • Purchasing stocks from different industries
  • Integrating different asset types into the stock portfolio
  • Rebalancing portfolios regularly
  • Monitoring and reassessing portfolios frequently

Optimal Portfolio Selection

  • It lies on the efficient frontier
  • It relies on an investor's risk aversion level
  • The point on the efficient frontier should be tangential to the investors indifference curve

Short Selling

  • Short selling refers to selling an asset not owned with the expectation of buying it back later at a lower price
  • Short selling simplifies minimization because it only leaves one contraint

Riskless Lending and Borrowing

  • A riskless asset has a fixed return over a period with zero risk
  • Riskless lending involves investing in a riskless asset with a fixed interest rate Rf
  • Riskless borrowing involves taking a loan at a fixed rate Rf

Efficient Frontier Cases

  • Case I: No short-selling, no riskless lending or borrowing; the EF is a constrained hyperbola
  • Case II: Short-selling is allowed, no riskless lending or borrowing; the EF is an unconstrained hyperbola
  • Case III: Short-selling, riskless lending, and borrowing are allowed; the EF is a straight line

The 2-Asset portfolio

  • Suppose asset 1 is risky, but asset 2 is risk free, then µp = x1µ1 + x2µ2, σp = x1σ1
  • Renaming asset 2 as asset f (where f means risk-free asset) µp = x1µ1 + (1 − x1)*Rf, σp = x1σ1
  • Does an investor prefer portfolios along RfA, RfB, or RfT : RfT is best
  • An efficient investment consists of lending or borrowing at a risk-free rate Rf and investing the remaining wealth in a tangency portfolio T

One-Fund Theorem

  • A single fund of assets T must be constructed for all investors efficient portfolios
  • All efficient portfolios are combinations of T and Rf assets

Modern Portfolio Theory

MPT Learning Outcomes

  • One will learn the fundamental assumptions underlying Modern Portfolio Theory (MPT)
  • Gain familiarity with different portfolio definitions, such as a portfolio, an opportunity set, an efficient portfolio, and the efficient frontier
  • Learn to calculate the expected return and variance and how correlation affects portfolio variance
  • Understand why utility theory differs from the mean-variance and can give more specific portfolio choices

Investment Portfolio Definition

  • A diversified securities collection in which xi is the weight and N is the total number of holdings

Return on a Portfolio

  • Rp = ∑i xiRi

Specification of Opportunity Set

  • specifying the investment universe, i.e., specifying the stocks i = 1, . . ., N that are available
  • estimate securities’ risk characteristics, i.e. expected return and variance.

MPT Assumptions

  • Investment decisions occur in a single time-period
  • Asset risk can be represented by means and variance.
  • Investors prefer non-satiation
  • Investor risk aversion

What is An Efficient Portfolio

  • Having less variance and higher expected returns

Expected Utility

  • Indifference emerges when numerous assets have the same anticipated utility
  • With indifference curves, higher expected utility are above and to the left

Correlation Effect

  • Correlation doesn't affect projected returns, however it does affect risk
  • The variance depends mostly on correlation of assets in a portfolio
  • Perfect positive correlation = p is 1
  • Perfect negative correlation = p is −1

Combining MPT and Utility Theory

  • MPT will identify a number of efficient portfolios that can be used
  • With utility theory applied, one single portfolio of investments is considered to be the most optimum

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