Shortly after the Gardners launched the Foolish Four Strategy, two skeptical finance professors tested it using data from the years 1949–72, just prior to the period data mined by the Gardners. It didn’t work. The professors also retested the Foolish Four Strategy during the years that were data mined by the Gardners, but with a clever twist. Instead of choosing the portfolio on the first trading day in January, they implemented the strategy on the first trading day of July. If the strategy has any merit, it shouldn’t be sensitive to the starting month. But, of course, it was.
