A random Walk Down Wall Street: The Time-Tested Strategy for Successful Investing

January Effect
A number of researchers have found that January has been
a very unusual month for stock-market returns. Stock-market
returns have tended to be especially high during the first two
weeks of January. The effect appears to be particularly
strong for smaller firms. Even after adjusting for risk, small
firms appear to offer investors abnormally generous returns
—with the excess returns largely produced during the first
few days of the year. Such an effect has also been
documented for several foreign stock markets. This led to the
publication of one book with the provocative title 
The
Incredible January Effect
. Investors and especially
stockbrokers, with visions of large commissions dancing
around in their heads, designed strategies to capitalize on this
“anomaly” believed to be so dependable.
One possible explanation for a January Effect is that tax

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effects are at work. Some investors may sell securities at the
end of the calendar year to establish capital losses for income
tax purposes. If this selling pressure temporarily depresses
stock prices, a bounce-back during the first week in January
could create abnormal returns. Although this effect could be
applicable for all stocks, it would be larger for small firms
because stocks of small companies are more volatile and less
likely to be in the portfolios of tax-exempt institutional
investors. Unfortunately, however, the transactions costs of
trading in the stocks of small companies are substantially
higher than those for larger companies (because of higher bid-
asked spreads and lower liquidity), and there appears to be
no way any ordinary investor could exploit this anomaly.
Moreover, the effect is not dependable in each year. In other
words, the January “loose change” costs too much to pick up
and in some years it turns out to be a mirage.