He then ran those firms through an array of tests involving their balance sheets and income statements, using such metrics as the return on assets rate, current ratio, change in gross margin, and change in asset turnover. The Piotroski F-score is a 9-point valuation metric derived on this research. Through back-testing, Piotroski found that buying the top stocks in the market according to his methodology and shorting those that got the worst scores would have resulted in 23% annualized gains from 1976 through 1996, more than double the S&P 500 broad market index return. His findings were made available to a wider audience via SmartMoney magazine and Bloomberg BusinessWeek.