1 / 94

REVIEW OF COVARIANCE

REVIEW OF COVARIANCE. Consider an asset A, whose expected return is k a . k a is an unknown variable, BUT with a known probability distribution. e.g. Treasury Bill Amazon.com. Probability distribution. Amazon. T-Bill. Rate of return (%). -70. 2. 15. 100. Expected Rate of Return.

nusa
Download Presentation

REVIEW OF COVARIANCE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. REVIEW OF COVARIANCE • Consider an asset A, whose expected return is ka. • ka is an unknown variable, BUT with a known probability distribution. • e.g. Treasury Bill • Amazon.com

  2. Probability distribution Amazon T-Bill Rate of return (%) -70 2 15 100 Expected Rate of Return

  3. What’s the formula for the standard deviation and variance?  = Standard deviation .

  4. What’s the formula for the Covariance?  = Covariance (kai - ka)(kbi - kb) Pi

  5. COVARIANCE • If A and B move up and down together, • the covariance will be positive. • If A and B move counter to one another, • the covariance will be negative • If A and B move with no relation, • the covariance will be small.

  6. COVARIANCE • If the return on either stock is highly uncertain, • cov will tend to be large, but a random relation may cancel this. • If either stock has zero STD DEV, • COV will be zero.

  7. COVARIANCE SUMMARY • COV(A,B) will be large and positive if: returns on assets have large standard deviations and move together. • COV(A,B) will be large and negative if: returns on assets have large standard deviations and move counter to one another.

  8. COVARIANCE SUMMARY • COV(A,B) will be tend to be small if: • returns move randomly, rather than up and down with one another; and/or either has a small standard deviation.

  9. How do you know if the covariance is large?

  10. CORRELATION COEFFICIENT • rab = COV(A,B) • StdDev(A)xStdDev(B) • COV(A,B)=rab [StdDev(A)xStdDev(B)] • SCATTER DIAGRAMS

  11. ka kb

  12. ka kb

  13. ka kb

  14. PORTFOLIO VARIANCE: TWO ASSET CASE • VAR(P) = (x2)Var(A) + (1-x)2Var(B) + (2)(x)(1-x) COV(A,B) • where • x=proportion of portfolio in Asset A

  15. PORTFOLIO VARIANCE: THREE ASSET CASE • VAR(P) = (xA)2 Var(A) + (xB)2Var(B) + (xC)2Var(C) + 2 xAxB cov(A,B)+ 2 xAxC cov(A,C) + 2 xBxC cov(B,C) • where • xA = proportion in asset A • xB = proportion in asset B • xC = proportion in asset C • (xA + xB+ XC) =1 • n.b. there are nc2 covariance terms.

  16. CHAPTER 4 Risk and Return: The Basics • Strange event in intellectual history • Basic return concepts • Basic risk concepts • Stand-alone risk • Portfolio (market) risk • Risk and return: CAPM/SML

  17. What are investment returns? • Investment returns measure the financial results of an investment. • Returns may be historical or prospective (anticipated). • Returns can be expressed in: • Dollar terms. • Percentage terms.

  18. What is the return on an investment that costs $1,000 and is soldafter 1 year for $1,100? • Dollar return: $ Received - $ Invested $1,100 - $1,000 = $100. • Percentage return: $ Return/$ Invested $100/$1,000 = 0.10 = 10%.

  19. What is investment risk? • Typically, investment returns are not known with certainty. • Investment risk pertains to the probability of earning a return less than that expected. • The greater the chance of a return far below the expected return, the greater the risk. • Since investors are risk averse, an asset with a larger std.dev. Implies a greater investment risk.

  20. Probability distribution Stock X Stock Y Rate of return (%) -20 0 15 50 • Which stock is riskier? Why?

  21. Minicase 4p.168 Simple?

  22. Assume the FollowingInvestment Alternatives

  23. What is unique about the T-bill return? • The T-bill will return 8% regardless of the state of the economy. • Is the T-bill riskless? Explain.

  24. Do the returns of Alta Inds. and Repo Men move with or counter to the economy? • Alta Inds. moves with the economy, so it is positively correlated with the economy. This is the typical situation. • Repo Men moves counter to the economy. Such negative correlation is unusual. • Market portfolio: ? • American Foam: ? See graph AM F

  25. Calculate the expected rate of return on each alternative. ^ r = expected rate of return. ^ rAlta = 0.10(-22%) + 0.20(-2%) + 0.40(20%) + 0.20(35%) + 0.10(50%) = 17.4%. See minicase 4

  26. ^ • Alta has the highest rate of return. • Does that make it best? Sumproduct function

  27. What is the standard deviationof returns for each alternative?

  28. T-bills = 0.0%. Repo = 13.4%. Am Foam = 18.8%. Market = 15.3%. Alta = 20.0%. Alta Inds:  = ((-22 - 17.4)20.10 + (-2 - 17.4)20.20 + (20 - 17.4)20.40 + (35 - 17.4)20.20 + (50 - 17.4)20.10)1/2 = 20.0%.

  29. Prob. T-bill Am. F. Alta 0 8 13.8 17.4 Rate of Return (%)

  30. Standard deviation measures the stand-alone risk of an investment. • The larger the standard deviation, the higher the probability that returns will be far below the expected return. • Coefficient of variation is an alternative measure of stand-alone risk.

  31. Expected Return versus Risk Can any of these be excluded? See Spreadsheet Chart: Northwest Rule in Graph-Investments

  32. It is tempting to say that T-Bills are least risky and HT is most risky; but • Before reaching a conclusion, we must consider: • magnitudes of expected returns (thus C.V) • skewness of distributions • our confidence in the prob. distributions • relationship between each asset and other assets that might be held.

  33. Coefficient of Variation (CV) Standardized measure of dispersion about the expected value: Std dev  CV = = . ^ Mean k Shows risk per unit of return.

  34. Asset X KX = 30% StdDev(X)= 10% Asset Y KY = 10% StdDev(Y)= 5% Example illustrating C.V.Consider two Assets: X & YWhich has more risk?

  35. Asset X KX = 30% StdDev(X)= 10% What is the probability that each asset will have a return < 10%? Asset Y KY = 10% StdDev(Y)= 5% Example illustrating C.V.Consider two Assets: X & YWhich has more risk?

  36. Asset X KX = 30% StdDev(X)= 10% CV(X)=.10/.30=.33 Asset Y KY = 10% StdDev(Y)= 5% CV(Y)=.05/.10=.5 Example illustrating C.V.Consider two Assets: X & YWhich has more risk?

  37. X Y 0 X>Y , but Y is riskier. Or Alternative Graph  : CVY> CVX. ^ k

  38. 30% 10% 0%

  39. Coefficient of Variation:CV = Standard deviation/expected return CVT-BILLS = 0.0%/8.0% = 0.0. CVAlta Inds = 20.0%/17.4% = 1.1. CVRepo Men = 13.4%/1.7% = 7.9. CVAm. Foam = 18.8%/13.8% = 1.4. CVM = 15.3%/15.0% = 1.0.

  40. Expected Return versus Coefficient of Variation

  41. Return vs. Risk (Std. Dev.): Which investment is best?

  42. Portfolio Risk and Return Assume a two-stock portfolio with $50,000 in Alta Inds. and $50,000 in Repo Men. ^ Calculate rp and p.

  43. Portfolio Return, rp ^ ^ rp is a weighted average: n ^ ^ rp = wiri i = 1 ^ rp = 0.5(17.4%) + 0.5(1.7%) = 9.6%. ^ ^ ^ rp is between rAlta and rRepo.

  44. Alternative Method Estimated Return ^ rp = (3.0%)0.10 + (6.4%)0.20 + (10.0%)0.40 + (12.5%)0.20 + (15.0%)0.10 = 9.6%. (More...)

  45. p = ((3.0 - 9.6)20.10 + (6.4 - 9.6)20.20 + (10.0 - 9.6)20.40 + (12.5 - 9.6)20.20 + (15.0 - 9.6)20.10)1/2 = 3.3%. • p is much lower than: • either stock (20% and 13.4%). • average of Alta and Repo (16.7%). • The portfolio provides average return but much lower risk. • Reason: ? • See spreadsheet for alternate calculation.

  46. Two-Stock Portfolios • Two stocks can be combined to form a riskless portfolio if r = -1.0. • Risk is not reduced at all if the two stocks have r = +1.0. • In general, stocks have r 0.65, so risk is lowered but not eliminated. • Investors typically hold many stocks. • What happens when r = 0?

  47. General Statements About Risk • Most stocks are positively correlated. rk,m 0.65. • 35% for an average stock. • Combining stocks generally lowers risk.

  48. DIGRESSION:CONSIDER TWO STOCKS: W & M

  49. CONSIDER TWO STOCKS: W & M

  50. W&M: rWM = -1.0

More Related