NBER
Working
Paper
#3154
October
1989
STOCK
MARKET
FORECASTABILITY
AND
VOLATILITY:
A STATISTICAL
APPRAISAL
ABSTRACT
This
paper
presents
and
implements
statistical
tests
of
stock
market
forecastability
and
volatility
that
are
immune
from
the
severe
statistical
problems
of
earlier
tests.
Although
the
null
hypothesis
of
strict
market
efficiency
is
rejected,
the
evidence
against
the
hypothesis
is
not
overwhelming.
That
is,
the
data
do
not
provide
evidence
of
gross
violations
of
the
conventional
valuation
model.
N.
Gregory
Mankiw
Department
of
Economics
Harvard
University
Cambridge,
MA
02138
(617)495-4301
David
Romer
Department
of
Economics
University
of
California
Berkeley,
CA
94720
(415)642-1785
Matthew
D.
Shapiro
Department
of
Economics
University
of
Michigan
Ann
Arbor,
MI 48109
(313)764-5419