Capital market efficiency

1. Lahore Business School
Subject: CAPITAL MARKETS AND EFFICIENCY
Student Names: Lamin Dampha, Khaleeq Ahmad
& Aniku Ahmed
Course Instructor: Prof. Dr. Ahmad Raza Bilal

2. Debate: Random Walk Theory
Title: Argument against the Random Walk Theory
which is duly supported by the literature

3. Introduction
A random walk is defined by the fact that price changes are independent of
each other (Brealey et al, 2005).
For a more technical definition, Cuthbertson and Nitzsche (2004) define a
random walk with a drift (δ) as an individual stochastic series Xt that behaves
as:
The drift is a simple idea. It is merely a weighted average of the probabilities
of each price the stock price could possibly move to in the next period. For
example, if we had €100 and this moved either 3.0% up or 2.5% down with
P=0.5 for each case, then the drift would be 0.25%, calculated by (Brealey et
al, 2005): 0.5(0.03) + 0.5(-0.025) = 0.0025 = 0.25%

4. Introduction
The Random Walk Theory is a popular theory in finance that
argues that stock prices and other financial assets move
randomly and therefore cannot be predicted or forecasted
based on past trends or data.
However, there are several strong arguments against the
Random Walk Theory that suggest that financial markets are
not as random as the theory claims.

5. Financial Markets are not Completely Efficient
The Random Walk Theory is based on the efficient market
hypothesis, which assumes that financial markets are
completely efficient and that all available information is
already reflected in the current market price of an asset.
However, empirical studies have shown that financial
markets are not completely efficient, and there is still some
room for profit through the exploitation of market
inefficiencies. For example, studies have shown that
momentum and value-based trading strategies have
consistently outperformed the market, suggesting that there
are exploitable market inefficiencies.

6. Market Psychology Plays a Role
The Random Walk Theory assumes that market participants
are rational and always act in their best interests, leading to
a completely random and unpredictable market.
However, behavioral finance studies have shown that
market psychology and emotions play a significant role in
financial decision-making, leading to market trends and
patterns that can be predicted and exploited. For example,
the herd mentality can lead to market bubbles and crashes,
which are not entirely random.

7. Technical Analysis Can Predict Market Trends
The Random Walk Theory argues that technical analysis,
which involves using past price data and chart patterns to
predict future market trends, is useless because market
movements are entirely random.
However, empirical studies have shown that technical
analysis can be a useful tool in predicting market trends and
identifying market inefficiencies. For example, studies have
shown that technical analysis can be used to identify
momentum and trend-following patterns, which have been
shown to be profitable trading strategies.

8. Financial Markets are Affected by External
Factors
The Random Walk Theory assumes that financial markets
are entirely self-contained and do not react to external
factors such as macroeconomic news or geopolitical events.
However, empirical studies have shown that financial
markets are significantly affected by external factors, leading
to predictable market trends and patterns. For example,
studies have shown that macroeconomic news releases such
as employment and inflation reports can significantly affect
market movements, suggesting that financial markets are
not entirely random.

9. Arguments against the Random Walk Model
There has been myriad of empirical research done into
whether there is predictability in stock prices. Below, a
summary of the main theories will be presented.

10. Short-Run and Long-Run Serial Correlations
and Mean Reversion
Lo and MacKinley (1999) suggest that stock price short-run serial
correlations are not zero. They also propose that in the short-run
stock prices can gain momentum due to investors ‘jumping on
the bandwagon’ as they see several consecutive periods of same-
direction price movement with a particular stock.
Shiller (2000) believes it was this effect that led to the irrational
exuberance of the dot-com boom.
However, in the long run, this does not continue and in fact, we
see evidence of negative autocorrelation. This has been dubbed
‘mean reversion’ and although some studies (e.g. Fama and
French (1988)) found evidence of it, its existence is controversial
as evidence has not been found in all research.

11. Market Over- and Under-reaction
Fama (1998) argues that investors initially over or under-react to the
information and the serial correlation explained above is due to them
fully reacting to the information over time. The phenomenon has also
been attributed to the ‘bandwagon effect’. Hirshleifer discusses
‘conservatism’ and argues that “under appropriate circumstances
individuals do not change their beliefs as much as would a rational
Bayesian in the face of new evidence” (Hirschleifer, 2001:1533). He
asserts that this could lead to over-reaction or underreaction.

12. Seasonal Trends
Here, evidence is found of statistically significant differences in
stock returns during particular months or days of the week.
The ‘January effect’ is the most researched, but Bouman and
Jacobsen (2002) also find evidence of lower market returns in the
months between May and October compared with the rest of
the year.
One problem with finding patterns in stock market movements
is that once found, they soon disappear. This seems to have been
the case with the January effect, as traders quickly eliminated
any profitable opportunities present because of the effect.

13. Size
Fama and French (1993) found evidence of a correlation
between the size of a firm and its return.
It appears that smaller, perhaps more liquid firms, garner a
greater return than larger firms.

14. Dividend Yields
Some research has been done on the ability of initial dividend
yields to forecast future returns.
As can be seen from Figure.3, generally a higher rate of return is
seen when investors purchase a market basket of equities with a
higher initial dividend yield.
It should be noted that this trend does not work dependably
with individual stocks.

15. Values vs Growth firms
It has been noted by many that in the long-term, value (low
price to earnings (P/E) and price to book-value (P/BV) ratios)
firms tend to generate larger returns than growth (high P/E and
P/BV ratios) firms.
In addition, Fama and French (1993) found there to be good
explanatory power when the size and P/BV were used
concurrently.

16. Conclusion
In conclusion, while the Random Walk Theory is a popular
theory in finance, there are several strong arguments against
its assumptions.
Financial markets are not entirely efficient, market
psychology plays a significant role, technical analysis can
predict market trends, and financial markets are affected by
external factors.
Therefore, it is essential to consider these factors when
making financial decisions, rather than relying solely on the
assumptions of the Random Walk Theory.

17. The End