In: Finance
Compare two cases
all portfolio weights are non-negative with the min SD
allow portfolio weights to be negative with the min SD
In the first case, if the portfolio weights are non-negative with the minimum SD, the SD will be lower. This is because the SD of the assets (with minimum SD) will have a higer proportion in the portfolio thereby, lowering the overall volatility (or SD ).
However, if the assets with minimum SD are allowed to have neagtive weights, meaning the weight of risky assets will be higher, that would increase the overall volatility (or SD) of the portfolio.
Example: A is a less risky asset (min SD) and weights are positive, the SD of the portfolio = 11 %
Assets | Return | SD | Weight | Expected Return | SD of the portfolio |
A | 10 | 5 | 0.4 | 16 | 11 |
B | 20 | 15 | 0.6 |
If A's weight becomes negative, SD of portfolio = 17%
Assets | Return | SD | Weight | Expected Return | SD of the portfolio |
A | 10 | 5 | -0.2 | 22 | 17 |
B | 20 | 15 | 1.2 |
Note: SD of the portfolio is calculated as =