The efficient market hypothesis is based on the presumption that rational
investors prevent price bubbles by trading against mispricing. In this paper,
we study the behavior of some of the most sophisticated investors during a
bubble period. Specifically, we analyze stock holdings of hedge funds during
the technology bubble, 1998–2000. We establish two main facts.
First, hedge funds were riding the technology bubble, not attacking it. On average,
hedge fund stock portfolios were heavily tilted toward technology stocks.
This suggests that short-sales constraints, emphasized in recent work on the
technology bubble (Ofek and Richardson (2003), Cochrane (2002)), are not sufficient
to explain the failure of rational speculative activity to contain the technology
bubble. Short-sale constraints and arbitrage risks alone can rationalize
reluctance to take short positions, but do not explain why sophisticated investors
would buy into the overpriced technology sector.
Second, on a stock-by-stock basis, hedge funds reduced their holdings before
prices collapsed. Within the technology segment—and only there—they outperformed
standard characteristics-matched benchmarks. This suggests that
hedge fund managers understood that prices of these stocks would eventually
deflate. Our findings are consistent with the view that the investor sentiment
driving the technology bubble was predictable to some extent, and that hedge
funds were exploiting this opportunity. Under these conditions, riding a price
bubble for a while can be the optimal strategy for rational investors, as, for
example, in AB (2003).