People love rules of thumb. Sometimes, mental shortcuts are helpful. Other times they are not. When it comes to investing, seasonal shortcuts are not uncommon. In fact, January boasts two: The January Effect explains why U.S. smaller company stocks tend to outperform the market in January. The original theory held that tax-loss harvesting pushed stock prices lower in December, making shares more attractive to investors in January. An article published in International Journal of Financial Research explained the effect could also owe something to the optimism that accompanies a new year, as well as year-end cash windfalls . In his book, A Random Walk Down Wall Street , Burton Malkiel described the January Effect this way, “…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.” The January Barometer suggests the performance of stocks during the first month...