Piotroski first published his now well known ratio in this famous research paper.

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Companies with a score of 8 or 9 have been found as a group to outperform weak stocks by 7.5% annually over a 20 year period. The weakest stocks, scoring 2 or lower, were found by Piotroski to be five times more likely to fall into financial problems.

Adding to this, he found in his paper that for groups of companies with high F-Scores, the entire distribution of returns was shifted to the right, successfully eliminating many of the worst losers from the group of stocks.