Savva Shanaev of Northumbria University and two colleagues mapped a century’s worth of U.S. stock-market returns against the annual predictions of Punxsutawney Phil, the star of the long-standing North American custom of Groundhog Day. According to the tradition, if the Pennsylvanian groundhog sees his shadow on February 2, winter will last for six more weeks. If he doesn’t, spring is around the corner—and, the researchers found, the market gets a boost. The conclusion: When the groundhog predicts an early spring, investors get optimistic.
A version of this article appeared in the January–February 2023 issue of Harvard Business Review.
