Who was Ralph Wanger?
Ralph Wanger (1934–2020) ran the Acorn Fund from its 1970 launch until he retired in 2003, compiling one of the longest and most respected records in small-company investing. He set out his method in A Zebra in Lion Country (1997), whose title carries the metaphor he built his career on: professional money managers behave like zebras in a herd. The animals in the middle are safe but eat trampled grass; the ones at the edge get the fresh grass, and also face the lions. Wanger fed at the edge. He looked for sound small-cap companies the crowd had ignored, and the Wanger (Revised) Screen is AAII's attempt to turn that instinct into rules.
The core idea
Wanger said the companies he owned rested on a solid tripod: growth potential, financial strength, and fundamental value. He started top-down, identifying social, economic, or technological themes he expected to run for at least one business cycle — four or five years — then bought the companies positioned to benefit. Often that meant investing downstream from a trend rather than in it: the banks that gained from ATMs, not the technology firms fighting each other to build them. He wanted a durable niche that kept competitors out, a balance sheet strong enough to fund growth without strain, and, above all, a reasonable entry price. That last piece is growth at a reasonable price, measured here through the ratio of the price-earnings multiple to the earnings growth rate — a PEG discipline that keeps a good business from becoming a bad investment.
What the Wanger (Revised) Screen looks for
- Market capitalization between $100 million and $2 billion at the most recent fiscal quarter — small enough to still have room to grow, but above the micro-cap range Wanger judged too risky.
- Listed on a major exchange rather than traded over the counter (OTC) — a floor on company size, share availability, and financial strength.
- The stock has traded for at least five years, meaning its price five calendar years ago was above zero — no IPOs, start-ups, or unproven turnarounds.
- Operating margin over the last 12 months above the industry median, so the strength shows up relative to peers rather than as a high absolute number that means little across industries.
- That same trailing-12-month operating margin at or above the company's own three-year average — the edge is current, not a fading one-time result.
- Sales growth over the last 12 months at least as fast as the annualized sales growth of the past three years, and above the industry median for the same period.
- A positive annualized sales growth rate over the past three years.
- Positive cash from operations over the last 12 months and in each of the last three fiscal years — real cash standing behind the reported profits.
- Total liabilities as a share of total assets below the industry median, a broad balance-sheet test that captures more than long-term debt alone.
- A current ratio above 1 for the latest quarter and for each of the last three fiscal years, so current assets consistently exceed current liabilities.
- A PEG ratio — the price-earnings ratio divided by five-year earnings-per-share growth — at or above 0.2 and below 1, buying growth at a discount to its own growth rate while screening out unsustainably high growth and the deepest low-P/E value traps.
The evidence, and why it can work
Wanger pointed to decades of academic work showing that smaller stocks earned higher long-run returns than large caps, even after adjusting for their extra risk. His explanation was mechanical as much as statistical: a small company's share price can re-rate through four routes — earnings growth, an acquisition premium, buybacks, or a rising valuation multiple as institutions take notice — while a mega-cap usually only gets the buyback. The screen tries to isolate the small caps most likely to travel one of those roads: profitable, growing faster than their industry, funded by real cash flow, and cheap against their own growth rate.
What to keep in mind
AAII has been candid that its revised interpretation underperformed the S&P 600 SmallCap index over long stretches, so treat the output as a starting list, not a verdict. Small caps trade thinly, spreads are wide, and the group can lag larger stocks for years at a time — which is why Wanger held positions for years and warned that cheap low-P/E stocks often become cheaper. The 0.2 floor on the PEG ratio is his hedge against growth rates too high to last. Read the story behind each name, confirm the niche is real, and size positions for a long, patient hold.
Sources
A Zebra in Lion Country: Ralph Wanger's Investment Survival Guide, Ralph Wanger with Everett Mattlin, Simon & Schuster, 1997.
American Association of Individual Investors (AAII) — Stock Investor Pro screen definition and commentary.