G. Cadogan
posted by gocadog
(8 January 2012)
other
(145 views, 54 downloads, 1 comments )
We present conditions under which positive alpha exists in the realm of active portfolio management–
in contrast to the controversial result in (Jarrow, 2010, pg. 20) which implicates delegated portfolio
management by surmising that positive alphas are illusionary. Specifically, we show that the critical
assumption used in (Jarrow, 2010, pg. 20), to derive the illusionary alpha result, is based on
a zero set for CAPM with Lebesgue measure zero. So conclusions based on the assumption may
well have probability measure zero of occurrence. Technically, the existence of [Tanaka] local time
on that set implies existence of positive alphas. In fact, we show that positive alpha exists under
the same scenarios of ”perpetual event swap” and ”market systemic event” Jarrow (2010) used to
formulate the illusionary positive alpha result. First, we prove that as long as asset price volatility
is greater than zero, systemic events like market crash will occur in finite time almost surely. Thus
creating an opportunity to hedge against that event. Second, we find that Jarrow’s ”false positive
alpha” variable constitutes portfolio manager reward for trading strategy. For instance, we show
that positive alpha exists if portfolio managers develop hedging strategies based on either (1) an
exotic [barrier] option on the underlying asset–with barrier hitting time motivated by the ”market
systemic” event, or (2) a swaption strategy for the implied interest rate risk inherent in Jarrow’s
triumvirate of riskless rate of return, factor sensitivity exposure, and constant risk premium for a
perpetual event swap.
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Godfrey, if the market is essentially complete and equilibrium characterizes asset prices, I'm not sure whether "alpha return" would not be illusionary in that instances... moreover, in continuous time, I'm not sure whether the cost of maintaining your "hedged" trading strategy would not lead to "vanishing alpha" or a ruin a la LTCM!