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CHAPTER 8. Index Models. Single-Index Model (Market Model). Suppose r i = a i + β i r M , (1) a i = a component of security i’s return that is not related to the market return; r M = the market return;
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CHAPTER 8 Index Models
Single-Index Model (Market Model) Suppose ri = ai + βi rM, (1) ai = a component of security i’s return that is not related to the market return; rM = the market return; βi = the sensitivity of security i’s return to the market return. Let ai = αi + ei , where αi = E(ai) (2) Substituting (2) into (1), we have ri = αi + βi rM + ei ,
Single-Index Model (Market Model) ri = αi + βi rM + ei , ri = stock i’s return rM = market return βi = sensitivity of stock i’s return to the market return ei = return component due to stock specific events
Market Model vs Portfolio Analysis From ri = αi + βi rM + ei and rj = αj + βj rM + ej COV(ri rj) = COV(αi + βi rM + ei , αj + βj rM + ej) = COV(βi rM, βj rM) = βi βj COV(rM, rM) = βi βj VAR(rM) Hence, бij2 = βi βj бM2 VAR(ri) = COV(αi + βi rM + ei , αi + βi rM + ei) = COV(βi rM + ei , βi rM + ei) Hence, бi2 = βi2бM2 + б2(ei)
Portfolio Optimization Problem Max θ = [E(rM) – rf]/ бM where E(rM) = Σwi E(ri) бM2 = ΣΣwiwj бi,j Σwi = 1 Input data: E(ri), rf, бi,j Number of input data = n + 1 + (n2 – n)/2 + n = (n +1)(1 + n/2)
Number of input data under the assumption of the market model Input data: E(ri), rf, βi,бM2,б2(ei) = n + 1 + n + 1 + n = 3n + 2
Single-Index Model Regression Equation: Rit = αi + βi RMt + eit where Rit = rit – rft and RMt = rMt - rft
Figure 8.2 Excess Returns on HP and S&P 500 April 2001 – March 2006
Figure 8.3 Scatter Diagram of HP, the S&P 500, and the Security Characteristic Line (SCL) for HP
Table 8.1 Excel Output: Regression Statistics for the SCL of Hewlett-Packard