The following is excerpted from the Validea Hot List newsletter published on March 4, 2011.

For decades, the price-to-earnings ratio has been the most widely used valuation measure for stock investors, and a key tool in the arsenals of many of the gurus I follow. While legendary investors like Benjamin Graham, Peter Lynch, and John Neff all used the ratio differently, they and many others agreed that the ratio itself was a key to finding bargain-priced stocks. The investing public and media seems to share their view, with the P/E ratio having long been the only valuation metric that most newspapers include in their daily stock listings.

But in 1984, Kenneth Fisher sent a shockwave through the P/E-conscious investment world. Fisher — the son of Phillip Fisher, who is known as the “Father of Growth Stock Investing” — thought there was a major hole in the P/E ratio’s usefulness. Part of the problem, he explained in his book Super Stocks, is that earnings — even earnings of good companies — can fluctuate greatly from year to year. The decision to replace equipment or facilities in one year rather than in another, the use of money for new research that will help the company reap profits later on, and changes in accounting methods can all turn one quarter’s profits into the next quarter’s losses, without regard for what Fisher thought was truly important in the long term — how well or poorly the company’s underlying business was performing.

While earnings can fluctuate, Fisher found that sales were far more stable. In fact, he found that the sales of what he termed “Super Companies” — those that were capable of growing their stock price 3 to 10 times in value in a period of 3 to 5 years — rarely decline significantly. Because of that, he pioneered the use of a new way to value stocks: the price-to-sales ratio (PSR), which compared the total price of a company’s stock to the sales the company generated.

Fisher’s findings — and his results — helped make the PSR a common part of investment parlance, and helped make him one of the most well-known investors in the world. (He is a perennial member of Forbes’ list of “The 400 Richest Americans”, his money management firm oversees tens of billions of dollars, and he is one of Forbes’ longest running magazine columnists.) The common sense, mostly quantitative approach he laid out in Super Stocks also caught my attention, and led me to create my Fisher-based Guru Strategy.

It’s important to note that today, Fisher says his approach to investing has evolved quite a bit since Super Stocks. The key to winning big on Wall Street is knowing something that other people don’t, he believes, and when too many people became familiar with PSR investing, he says he needed to find other ways to exploit the market.

So why have I continued to use my Super Stocks-based model? Two reasons: First, Fisher’s publisher reissued the book in 2007, with the same PSR focus. Second, the strategy flat out works. From its July 2003 inception through the end of 2010, my 10-stock Fisher-based portfolio gained 163.9% (13.9% annualized), while the S&P 500 gained just 25.7% (3.1% annualized). That makes it one of my most successful long-term strategies.

Price-to-Sales and “The Glitch”

Fisher is a student of investor psychology, and his observations about investor behavior are what led to his PSR discovery. Often, he found, companies will have a period of strong early growth and become the darlings of Wall Street, raising expectations to unrealistic levels. Then, they then have a setback. Their earnings drop, or continue to grow but simply don’t keep pace with Wall Street’s lofty expectations. Their stocks can then plummet as investors overreact and sell, thinking they’ve been led astray.

But while investors overreact, Fisher believed that these “glitches” are often simply a part of a firm’s maturation. Good companies with good management identify the problems, solve them, and move forward, and as they do the stock’s price begins to rise again. If you can buy a stock when it hits a glitch and its price is down, you can make a bundle by sticking with it until it rights the ship and other investors jump on board.

The key in all of this was finding a way to evaluate a firm when its earnings were down, or when it was losing money (remember, you can’t use a P/E ratio to evaluate a company that is losing money, because it has no earnings). The answer: by looking at sales, and the PSR.

According to the model I base on Fisher’s writings, stocks with PSRs below 1.5 are good values. And the real winners are those with PSR values under 0.75 — that’s the sign of a Super Stock. To find the PSR, Fisher says to take the total value of a company’s stock, i.e. its market cap (the per-share price multiplied by the number of shares outstanding). We then divide that number by the firm’s trailing 12-month sales.

One note: Because companies in what Fisher called “smokestack” industries — that is, industrial or manufacturing type firms that make the everyday products we use — grow slowly and don’t earn exceptionally high margins, they don’t generate a lot of excitement or command high prices on Wall Street. Their PSRs thus tend to be lower than those of companies that produce more exciting products, Fisher said. He adjusted his PSR target for these firms, and the model I base on his writings looks for smokestack firms with PSRs between 0.4 and 0.8; it is particularly high on those with PSR values under 0.4.

Beyond the PSR

While the PSR was key to Fisher’s strategy, he warned not to rely exclusively on it. Terrible companies can have low PSRs simply because the investment world knows they are headed for financial ruin.

Other quantitative measures Fisher used include profit margins (he wanted three-year average net margins to be at least 5 percent; the debt/equity ratio (this should be no greater than 40 percent, and is not applied to financial firms); and earnings growth (the inflation-adjusted long-term EPS growth rate should be at least 15 percent per year).

Fisher also made an interesting observation about companies in the technology and medical industries. He saw research as a commodity, and to measure how much Wall Street valued the research that a company did, he compared the value of the company’s stock (its market cap) to the money it spends on research. Price/research ratios less than 5 percent were the best case, and those between 5 and 10 percent were still indicative of bargains. Those between 10 and 15 percent were borderline, while those over 15 percent should be avoided.

One of the Best

The variety of variables in my Fisher-based model are a big part of why I think it continues to work, long after the PSR has become a well-known stock analysis tool. While it uses the PSR as its focal point, it also makes sure firms have strong profit margins, earnings growth, and cash flows, and low debt/equity ratios. That well-rounded approach helped it get through one of the worst periods for the broader market in history and stay far, far ahead of the market over the long haul — all while the PSR has been a well-known investing tool. I expect this solid approach will continue to pay dividends over the long haul.

Now, here’s a look at the stocks that currently make up my 10-stock Fisher-based portfolio.

1. China Integrated Energy Inc. (CBEH)
2. World Fuel Services Corporation (INT)
3. Clearwater Paper Corp. (CLW)
4. GameStop Corp. (GME)
5. Dollar Tree, Inc. (DLTR)
6. Ross Stores, Inc. (ROST)
7. Aeropostale, Inc. (ARO)
8. Telecom Argentina S.A. (TEO)
9. Fuel Systems Solutions, Inc. (FSYS)
10. Lincoln Educational Services (LINC)