Who is Joseph Piotroski, and what is the F-Score?
Joseph Piotroski is an accounting professor who built the strategy behind this screen in 2000, while teaching at the University of Chicago's Graduate School of Business; he later joined the faculty at Stanford. His paper — "Value Investing: The Use of Historical Financial Statement Information to Separate Winners from Losers," published in the Journal of Accounting Research — asked a narrow, useful question. Among cheap stocks, can ordinary financial-statement data tell the recovering companies apart from the ones still falling? His answer was the F-Score, a nine-point checklist that has become one of the most cited quality measures in quantitative value investing. The Piotroski High F-Score screen pairs that checklist with a strict cheapness filter.
The core idea: financial strength inside cheapness
Buying stocks with a low price-to-book-value ratio works on average, but the average hides a messy split. A basket of the cheapest stocks is crowded with genuinely distressed businesses, and a handful of big winners pulls the group's mean return upward while many of the names quietly lose money. Piotroski wanted to skim off the likely winners in advance.
His reasoning: these stocks are small, neglected, and barely followed by analysts, so simple accounting signals that a well-covered market would price in immediately still carry information here. Instead of forecasting earnings, he scored each firm on nine yes-or-no tests covering profitability, funding, and operating efficiency — one point per test, zero to nine. A high score of 8 or 9 marks a cheap company whose fundamentals are actually improving. A low score marks one that is still deteriorating, and probably cheap for good reason.
What the Piotroski High F-Score screen looks for
The screen first ranks the universe on price-to-book value and keeps only the cheapest fifth — the same high book-to-market stocks Piotroski studied. It then scores each survivor on the nine F-Score tests and demands a near-perfect result:
- Price-to-book-value ratio in the bottom 20% of the database — the cheapest fifth of stocks.
- American depositary receipts (ADRs) and over-the-counter (OTC) stocks are excluded, which screens out the least liquid and least consistently reported names.
- Profitability (four points): positive return on assets in the latest fiscal year; positive cash flow from operations; return on assets higher than the year before; and operating cash flow greater than net income (income after taxes) — an accrual check that rewards earnings backed by real cash.
- Leverage, liquidity and funding (three points): a lower long-term-debt-to-assets ratio than the prior year; a higher current ratio than the prior year; and shares outstanding no higher than the prior year, meaning the company did not raise money by issuing new stock.
- Operating efficiency (two points): gross margin higher than the prior year, and asset turnover higher than the prior year.
- To pass, a stock must clear at least eight of the nine tests — an F-Score of 8 or 9.
The evidence
Piotroski tested the score on high book-to-market firms from 1976 to 1996. Selecting the financially strong names lifted the mean return of a cheap-stock portfolio by at least 7.5% a year, and — more telling — shifted the entire distribution of outcomes to the right, trimming the tail of disasters rather than just raising the average. A long-short version, long the highest scorers and short the lowest, earned roughly 23% a year over that window. The improvement was concentrated in small, thinly traded, lightly followed firms, exactly where prices drift furthest from value. AAII's own screening results have echoed the pattern: the higher the score, the higher the average portfolio return.
What to keep in mind
The trait that makes the F-Score effective is also its main constraint. It works best among small, illiquid, beaten-down stocks — the very names that are hardest to buy in size without moving the price, and hardest to exit in a hurry. Treat the passing list as small-cap, and size positions accordingly.
It is also a quality filter, not a valuation or timing tool. The price-to-book rank supplies the cheapness; the score only sorts financial health within that cheap set. It never asks whether a stock is cheap enough, or when to buy. The nine tests read last year's statements, so they describe where a business has been, not where it is headed — and a company lapping one terrible year can flip several improvement tests at once without being durable. Pairing the book-to-market filter with a high score narrows the odds of a value trap; it does not erase them. Read the story behind each name before you buy.
Sources
Joseph D. Piotroski, "Value Investing: The Use of Historical Financial Statement Information to Separate Winners from Losers," Journal of Accounting Research, Vol. 38 (Supplement), 2000.
American Association of Individual Investors (AAII) — Stock Investor Pro screen definition and commentary.