Mark Hulbert writes in MarketWatch that “all of [the small-cap] sector’s much-vaulted historical relative strength has come at the end of December and early January,” as reflected in the monthly average outperformance of small-caps vs. large-caps 1926-2015. According to Dartmouth professor Ken French, small-caps usually hit a low around December 20, followed by the highest yields in January. The long-term outperformance by small caps is 2.2%, according to Ibbotson data. French’s day-by-day analysis suggests, however, that from late December to end of January the return is an average of 2.5%. Hulbert reminds investors that these are averages over 89 years for thousands of stocks, so “to bet on small-cap strength, you therefore need to diversify across many issues.”