Investopedia: What is the 'January Effect'?

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January Effect
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What is the 'January Effect'

The January effect is a seasonal increase in stock prices during the month of January. Analysts generally attribute this rally to an increase in buying, which follows the drop in price that typically happens in December when investors, engaging in tax-loss harvesting to offset realized capital gains, prompt a sell-off. Another possible explanation is that investors use year-end cash bonuses to purchase investments the following month.

BREAKING DOWN 'January Effect'
The January effect is a hypothesis, and like all calendar-related effects, suggests that the markets as a whole are inefficient, as efficient markets would naturally make this effect nonexistent. The January effect seems to affect small caps more than mid or large caps. Since the beginning of the 20th century, the data suggests that these asset classes have outperformed the overall market in January, especially toward the middle of the month.

Investment banker Sidney Wachtel first noticed this effect in 1942. This historical trend, however, has been less pronounced in recent years because the markets seem to have adjusted for it. Another reason analysts consider the January effect less important as of 2016 is that more people are using tax-sheltered retirement plans and therefore have no reason to sell at the end of the year for a tax loss.

Beyond tax-loss harvesting and repurchases, as well as investors putting cash bonuses into the market, another explanation for the January effect has to do with investor psychology. Some investors believe that January is the best month to begin an investment program or perhaps are following through on a New Year's resolution to begin investing for the future.
Studies and Criticism

One study, analyzing data from 1904 to 1974, concluded that the average return for stocks during the month of January was five times greater than any other month during the year, particularly noting this trend existed in small-capitalization stocks. The investment first Salomon Smith Barney performed a study analyzing data from 1972 to 2002 and found that the stocks of the Russell 2000 index outperformed stocks in the Russell 1000 index (small-cap stocks versus large cap stocks) in the month of January. This outperformance was by 0.82%, yet these stocks underperformed during the remainder of the year. Data suggest that the January effect is becoming increasingly less prominent.

An ex-Director from the Vanguard Group, Burton Malkiel, the author of "A Random Walk Down Wall Street", has criticized the January effect stating that seasonal anomalies such as it don't provide investors with any reliable opportunities. He also suggests that the January effect is so small that the transaction costs needed to exploit it essentially make it unprofitable.
Calendar Effect
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A collection of assorted theories that assert that certain days, months or times of year are subject to above-average price changes in market indexes and can therefore represent good or bad times to invest. Some theories that fall under the calendar effect include the Monday effect, the October effect, the Halloween effect and the January effect.
BREAKING DOWN 'Calendar Effect'

Most of the evidence for these effects is anecdotal, although there is a slight statistical case to be made for some of them, which is more than enough to encourage some investors to place their faith in them.

Proponents of the October effect, one of the most popular theories, argue that October is when some of the greatest crashes in stock market history, including 1929's Black Tuesday and Thursday and the 1987 stock market crash, occurred. While statistical evidence doesn't support the phenomenon that stocks trade lower in October, the psychological expectations of the October effect still exist.

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