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The January effect: Understanding the phenomenon in the stock market

By Kristoff De Turck

Last update: Feb 2, 2023

The January effect is a well-known stock market phenomenon that refers to the tendency of stock prices to rise at the beginning of the year. The effect is said to have the most impact on small-cap stocks because of their lower liquidity. The reason for this seasonal rise in stock prices is often attributed to a combination of factors that we will explain in this article.

What causes the January effect?

The January effect is a stock market phenomenon that occurs during the first trading days of the new year when stock prices rise significantly. The exact cause of the January effect is still debated among market experts.

However, it is generally believed to be a result of several factors, including tax loss sales, increased buying activity and window dressing by portfolio managers.

Tax-Loss Harvesting

One of the main factors contributing to the January effect is Tax-Loss Harvesting. This occurs when investors sell losing stocks in their portfolios to offset gains from other investments. This allows them to reduce their taxable income and lower their overall tax bill. This selling activity usually results in lower stock prices for these losing investments, which then leads to an increase in stock prices for other investments as buyers pounce on the lower prices.

Increased buying activity

Another factor contributing to the January effect is increased buying activity. As the new year begins, many investors receive year-end bonuses and other forms of income that they can use to invest in the stock market. This increased buying activity drives up demand for stocks, causing prices to rise.

This increased demand occurs especially in the markets for small-cap stocks, which tend to be less well tracked and less traded, making them more sensitive to price movements based on changes in demand.

Window Dressing by Portfolio Managers

The final factor contributing to the January effect is window dressing by portfolio managers. At the end of each quarter, many portfolio managers adjust their holdings in an attempt to make their portfolios look better. This often involves selling underperforming stocks and buying stocks that have performed well in recent months.

This buying activity can drive up prices, contributing to the January effect.

Statistical Evidence?

Substantial scientific research has already been done to find out whether or not there is any value behind this January phenomenon. And as with many studies, opinions are divided.

Still, more recent figures (source: Investopedia) show that the effect has largely faded away. Figures since 1993 to date show that in only 17 of 30 years the S&P500 index was able to end the first month on a positive note. This amounts to 57%. If we start from the beginning of the market uptrend since 2009 we obtain the same percentages. Out of 14 times, the S&P500 managed to close positive 8 times.

Given the enormous increase in prices since then, this is a relatively low result.

And what about “As January Goes, So Goes The Year”?

This is another popular stock market saying which is actually an extension of the January effect and states that the performance of the stock market in the month of January can be a good indicator of how the market will perform for the rest of the year. The idea is based on the belief that if the stock market performs well in January, it is likely to continue to perform well throughout the year. Moreover, it works both ways. A poor January is a harbinger of a negative stock market year.

Looking at the results since 1950, there indeed appears to be strong evidence for this theory. Including 2022 - where the negative January month indeed foreshadowed a negative year end - only 11 errors were recorded. This means that the prediction was correct in 85% of cases. Pretty impressive numbers!

Critics, however, argue that this does not prove causality at all because during the same period, U.S. equity markets generated positive returns roughly 70% of the time. In other words, the overall long-term trend has always been bullish since then and the so-called January signal is nothing but a secondary side-effect of that.

Whatever the case may be, the data behind this stock market wisdom has remained fairly robust to date, and the debate over whether or not it is causally related to the outcome of the rest of the year will always have its proponents and opponents.

The impact of the January effect on investors

Keep in mind that the January effect is a seasonal trend and not a guarantee, the more recent numbers show that the probability of a January effect is only slightly higher than flipping a coin. The contention that January is a harbinger for the rest of the year is supported by the data to this day but there is debate as to whether this is causal or rather a result of an already existing long-term bullish trend.

Whatever the case, as with any investment strategy, it is important to do thorough research and understand the risks before making an investment decision. In addition, investors should consider the potential impact of other market factors, such as economic conditions and changes in interest rates or market sentiment, which can also affect stock prices.

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