January barometer

How might stocks perform in 2019? Here's what this indicator says.

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A widely followed market theory, popularized by The Stock Trader's Almanac, claims that as January goes, so goes the full year. With January 2019 in the books, this indicator says investors may have cause to put 2018's turbulence in the past. But there are reasons to take the January barometer with a grain of salt.

An uncertain backdrop

In many respects, global stock markets are operating under an umbrella of uncertainty. Trade disputes, the US government shutdown, and the ongoing Brexit situation, among other economic and geopolitical developments, continue to loom over investors. These factors pressured stocks last year: The MSCI World Index decreased 10% and the S&P 500 lost 6%, on a price return basis.

However, some positive factors—like continued earnings strength, improved valuations, and a temporary deal to reopen the US government—helped stock markets bounce back at the start of 2019 (see US stocks were on the rise at the outset of 2019).

So, does this year's 8% January gain—well above the 1.1% average for the month of January since 1945—point to an up year for stocks? Momentum is one of the primary reasons why some investors give credence to indicators like the January barometer. The thought process here is that a bullish start to the year will set the market in the right direction, propelling it throughout the year. For example, in 2017, a 2% January gain for the S&P 500 preceded the 19% full-year rally. Of course, this pattern doesn't always hold: The S&P 500 lost 6% last year after gaining 6% in January.

A bullish start is the stronger predictor

Based solely on the past performance of the US market, an up January has generally been bullish for stocks. That has been particularly the case when the market has gained more than 5% in January. The January barometer has held true nearly 75% of the time when January experienced market gains since 1945. Notable exceptions followed extended periods of market growth.

Since 1946, a positive January for the S&P 500 has resulted in an average gain of 11.1% for the remaining 11 months, whereas a down January resulted in just a 1.3% gain for the remaining months, on average (see Average S&P 500 price change after positive/negative January).

It's worth noting that a down January has not been a reliable predictor of an overall weak year. Of course, historical trends are not a guarantee of what will happen in the future, and there are a myriad of other, more important fundamental factors to consider, including valuations, earnings strength, and fiscal and monetary policy, among others.

Cracks in the barometer

Why might up Januaries be better predictors than down ones? One reason may be the historical proclivity of stocks to rise. US stocks have finished higher in all but 17 out of 72 years since 1945. So, the fact that stocks finish higher for the year so often after both a positive and negative January may simply be the result of this directional bias.

Indeed, there is a very strong correlation between positive January S&P 500 performance and positive market performance for the entire year. During only 2 years have stocks dropped sharply (a price decline of more than 10% for the full calendar year) after a positive January, with both instances occurring at the end of powerful multiyear market advances (1966 and 2001).

Moreover, a down January may not be a reliable predictor of a weak year overall. Going back to 1950, in 12 out of 26 years when January finished in the red, the stock market actually ended higher, and often by a very substantial amount.

As previously mentioned, momentum is one possible reason that positive stock performance during January may actually be a reliable predictor for full-year performance. If the market gets off to a good start, a bullish trading pattern can form, and that can help fuel continued positive performance as investors jump on the trend. From a historical perspective, there appears to be no clear evidence as to why a negative start does not more strongly imply a negative year, compared with the high correlation of a positive January translating to a positive year. The full-year outcome after a negative January (or a positive January, for that matter) may simply be spurious.

First 5 days

In addition to the January barometer, some market watchers place particular emphasis on the first 5 trading days of January as an indicator of where the market is headed for the full year. The first 5 trading days of this year saw US stocks add 2.7%, pointing toward a potentially positive year for the market, according to this indicator. But you need only look to last year to see the cracks in this theory. During 2018, stocks gained 2.8% during the first 5 days before finishing the year in the red. One interesting recent occurrence where the first 5 days theory proved particularly unreliable was when stocks shed 4.8% during the first 5 days in 2016, the worst start ever on record. That ended up not being predictive, as stocks rebounded by that year's end.

A major problem with this theory is that the sample size of trading days is small (5), compared with the January barometer (typically about 20—which is also not a large sample size), to be a reliable predictor of the rest of the year. Given the small number of trading days associated with the first 5 days theory, there does not seem to be enough time for momentum to become a significant factor.

Investing implications

While it is impossible to predict the future, proponents of the January barometer think this indicator may provide some indication of how stocks will perform.

However, some of the evidence is not entirely conclusive. Additionally, each year is unique, as the factors impacting the market are constantly changing. For example, in recent days, the potential impact of the possibility of rising rates and higher inflation may have contributed to the increase in volatility seen in late January and early February. Many investors like following the January barometer because it provides an easily identified outcome. But beware: Crafting a strategy solely on this theory is not prudent.

Next steps to consider

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