Index

Topics: Variance, Sharpe ratio, Modern portfolio theory Pages: 4 (410 words) Published: April 13, 2014
17.a.
Alpha (α)
Expected excess return
αi = ri – [rf + βi × (rM – rf ) ]
E(ri ) – rf
αA = 20% – [8% + 1.3 × (16% – 8%)] = 1.6%
20% – 8% = 12%
αB = 18% – [8% + 1.8 × (16% – 8%)] = – 4.4%
18% – 8% = 10%
αC = 17% – [8% + 0.7 × (16% – 8%)] = 3.4%
17% – 8% = 9%
αD = 12% – [8% + 1.0 × (16% – 8%)] = – 4.0%
12% – 8% = 4%
Stocks A and C have positive alphas, whereas stocks B and D have negative alphas. The residual variances are:
2(eA ) = 582 = 3,364
2(eB) = 712 = 5,041
2(eC) = 602 = 3,600
2(eD) = 552 = 3,025

b.To construct the optimal risky portfolio, we first determine the optimal active portfolio. Using the Treynor-Black technique, we construct the active portfolio:

A
0.000476
–0.6142
B
–0.000873
1.1265
C
0.000944
–1.2181
D
–0.001322
1.7058
Total
–0.000775
1.0000
Be unconcerned with the negative weights of the positive α stocks—the entire active position will be negative, returning everything to good order.

With these weights, the forecast for the active portfolio is: α = [–0.6142 × 1.6] + [1.1265 × (– 4.4)] – [1.2181 × 3.4] + [1.7058 × (– 4.0)] = –16.90%
β = [–0.6142 × 1.3] + [1.1265 × 1.8] – [1.2181 × 0.70] + [1.7058 × 1] = 2.08 The high beta (higher than any individual beta) results from the short positions in the relatively low beta stocks and the long positions in the relatively high beta stocks. 2(e) = [(–0.6142)2×3364] + [1.12652×5041] + [(–1.2181)2×3600] + [1.70582×3025] = 21,809.6

 (e) = 147.68%
The levered position in B [with high 2(e)] overcomes the diversification effect, and results in a high residual standard deviation. The optimal risky portfolio has a proportion w* in the active portfolio, computed as follows:

The negative position is justified for the reason stated earlier. The adjustment for beta is:

Since w* is negative, the result is a positive position in stocks with positive alphas and a negative position in stocks with negative alphas. The position in the index...
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