In 2000, Stanford accounting professor Joseph Piotroski developed the F-score, which discriminates higher potential members within a class of value candidates. The F-score aims to discover additional value from signals in a firm's series of annual financial statements, after initial screening of static measures like book-to-market value. The F-score formula inputs financial statements and awards points for meeting predetermined criteria. Piotroski retrospectively analyzed a class of high book-to-market stocks in the period 1976-1996, and demonstrated that high F-score selections increased returns by 7.5% annually versus the class as a whole. The American Association of Individual Investors examined 56 screening methods in a retrospective analysis of the financial crisis of 2008, and found that only F-score produced positive results.