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Economics 434 Theory of Financial Markets Professor Edwin T Burton Economics Department The University of Virginia Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Modern Portfolio Theory Three Significant Steps to MPT Harry Markowitz Mean Variance Analysis The Concept of an “Efficient Portfolio” James Tobin What Happens When You Add a “Risk Free Asset” to Harry’s story Bill Sharpe (Treynor Lintner, Mossin, etal) Put Tobin’s Result in Equilbrium The Rise of Beta The Insignificance of “own variance” Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Need Some Statistics Mean, Variance, Covariance Standard Deviation Mean --- roughly means ‘average’ Variance – squared differences summed up Covariance – two variable, take differences of each from their means, multiply the differences observation by observation Standard Deviation = Square Root of Variance We will typically use normal distribution – but that is not necessary. We could use other distributions Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Because of uncertainty, we need a different utility function Why not just expected value? Instead, we use expected utility What’s the difference? Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 i 1 Some Definitions 2 i 1 n xi x x x n i n n 2 = √ 2 n x, y x ( x) y ( y ) i 1 n 1,2 Economics 434 – Financial Market Theory 1,2 12 Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Modern Portfolio Theory Randomness Construction of efficient (best) portfolios Harry Markowitz Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 How Do You Create A Portfolio? Try It with Two Assets Mean “X1” “X2” Where are the Portfolios That Can Be Created from Just These Two Assets ? Standard Deviation Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Back to the ½, ½ Portfolio Mean of X1 Mean of P Mean of X2 Economics 434 – Financial Market Theory Where P = ½ [X1] + 1/2 [X2] Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Variance of a Portfolio with two assets P2 = (P - P)2 n = {1(X1- 1) + 2(X2 - 2)}2 n Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Variance – with two assets 2 P 2 { (X ) + (X )} 1 1 1 2 2 2 = n = { (1)2[X1 - 1]2 + (2)2[X2 - 2]2} + 212(X1 - 1)(X2 - 2)} n Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Variance with 2 Assets Continued = {(1)2[X1 - 1]2 + (2)2[X2 - 2]2 n + 212(X1 - 1)(X2 - 2)} n Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Variance with 2 Assets - Continued = (1)212 + (2)222 + { 212(X1 - 1)(X2 - 2)} n = (1)212 + (2)222 + 212Cov (X1,X2) = (1)212 + (2)222 + 2121,2 Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Variance with 2 Assets - Continued = (1)212 + (2)222 + 2121,2 Recall the definition of the correlation coefficient: 1,2 1,2 12 = (1)212 + (2)222 + 2121,212 Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Variance with 2 Assets - Continued = (1)212 + (2)222 + 2121,212 where 1,2 1,2 12 What Happens if = 1? Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 If = 1 (1)212 + (2)222 + 2121,212 becomes = (1)212 + (2)222 + 21212 2P= (11 + 22)2 P= (11 + 22) Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 If = 1 P= (11 + 22) If 1 P (11 + 22) Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Back to the ½, ½ Portfolio If = 1 Mean of X1 Mean of P Mean of X2 Where P = ½ [X1] + 1/2 [X2] 1,2 = 1/21 + 1/22 Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 Back to the ½, ½ Portfolio If 1 1,2 1/21 + 1/22 Mean of X1 Mean of P Mean of X2 Economics 434 – Financial Market Theory Where P = ½ [X1] + ½ [X2] Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 If = 1 Then all the portfolios are here Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 If 1 Then all the portfolios are here Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 This Means the “boundary”of the possible portfolios looks like this: Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 This is very convenient Mean Maximizes Utility Standard Deviation Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009 The End Economics 434 – Financial Market Theory Tuesday, Tuesday, September August 24, 21,2010 2010 Tuesday, Sept 25, 2012 Tuesday, August 25, 2009