If you're a busy investor with more than just stock-picking on your plate, you might want to consider a mechanical investing strategy. And if you're interested in stocks, one of the most intriguing of these strategies is Joel Greenblatt's Magic Formula.

Greenblatt details this approach in his enriching, funny tome The Little Book That Beats the Market. His strategy revolves around two factors:

  • How cheap is the stock?
  • How profitable is the company?

This simplified approach really boils value investing down to its essence. When you find a company whose price fails to reflect its high profits, you might have a winner.

A cheap business and a profitable company
To find cheap companies, the Magic Formula looks for a high earnings yield -- basically, a company's EBIT divided by its enterprise value. EBIT is earnings before interest and taxes, otherwise known as operating earnings. Enterprise value includes the company's market capitalization and then adds its net debt. In general, the higher the earnings yield, the better.  The Magic Formula looks for a yield higher than 10%.

To find profitable companies, Greenblatt's Magic Formula seeks businesses that generate returns on assets greater than 25%. In other words, for every $100 in assets it holds, the company would produce at least $25 in net profit. In general, the higher the ROA, the better the business.  Greenblatt looks for companies with an ROA higher than 25%.

So how do these telecom companies fare?

Company

Enterprise Value

EBIT

Earnings Yield

ROA

Millicom International (Nasdaq: MICC) $12,660 $1,114 8.8% 10.5%
Telefonica (Nasdaq: TEF) $191,423 $19,006 9.9% 7.2%
France Telecom (Nasdaq: FTE) $107,684 $11,748 10.9% 5.9%
MetroPCS Communications (NYSE: PCS) $9,205 $721 7.8% 5.6%

Source: Capital IQ, a division of Standard & Poor's. Trailing-12-month figures.

Going by the Magic Formula criteria, none of these companies meets both standards.  Telefonica and France Telecom both are near or above the formula's desired 10% earnings yield, but they both have ROAs below 10%. MetroPCS is the lowest in both categories, with an earnings yield below 8% and an ROA below 6%. But even though they didn't meet the Magic Formula screen, that certainly doesn't mean they can't be profitable investments. These high-quality companies are rarely on sale, so they often won't make the Magic Formula cut.

Foolish bottom line
The key advantage of the Magic Formula is speedy decision-making. You can run a screen and mechanically buy the stocks, and then you can spend your free time doing the activities you love. However, such an approach means that you need to pick a lot of stocks (say, 25 or 30), since you haven't performed any strategic analysis of your investments. According to the formula, you should hold the stocks for one year to receive favorable tax treatment, sell all of them, and then run the screen again to find your new picks.

This approach sounds easy, but Greenblatt cautions that it can be tough to stick with during hard times. In some years, this mechanical strategy simply won't work. However, Greenblatt's extensive backtesting suggests that over the long haul, his Magic Formula can significantly outperform the market.

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Jim Royal, Ph.D., owns shares in France Telecom. The Motley Fool owns shares of Telefonica. Motley Fool newsletter services have recommended buying shares of France Telecom. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insightsmakes us better investors. The Motley Fool has a disclosure policy.