2.2. The imperfect substitutes and the downward-sloping Demand curve
for Stocks Hypothesis (DSH)
Stocks belonging to the index do not have perfect substitutes
and have downward-sloping demand curves. Prices will therefore
change to eliminate any excess demand in themarket and hence no reversal
is expected in the long-term. Abnormal trading activity should be
temporary, until the new level of price equilibrium is reached. Shleifer
(1986) and Wurgler and Zhuravskaya (2002) support the DSH. Morck
and Yang (2002) also found that S&P 500 membership was associated
with significantly higher valuations of member firms.