On the lneffrciency of Portfolio Insurance and Caveats to the Mean/Downside-Risk Framework

Portfolio insurance strategies based on options typically treat the investment in the risky asset, e.g., stock, as fixed. We show in a mean/downside-risk framework that such a strategy is inefficient. Using at the money put options, expected returns can be increased by more than 250 basis points without taking on more risk. Gains can become arbitrarily large when one uses options with extremely high strike prices. This is due to a serious caveat to the mean/downside-risk framework that is typically adopted in the literature by substituting downside-risk measures for standard risk measures such as the variance of returns. These pathologic results vanish when one maximizes an appropriately chosen HARA utility function. In this framework, fixing the holding of the risky asset in advance leads to efficiency losses that vary between 250 and 650 basis points depending on the degree of risk aversion.