In his latest RealMoney column, Validea CEO John Reese takes a look at Joel Greenblatt’s remarkably simple — and remarkably successful — investment strategy.

“For many years, I have been studying how great investors invest, and almost always, they use five or 10 or more variables, so they can look at a stock and its underlying company from a variety of perspectives,” writes Reese. “I’ve never seen an exceptional strategist use one variable, but there is one of note [Greenblatt] who uses just two, and this is as simple as stock analysis gets.”

Reese looks at the unique ways Greenblatt calculates those two metrics — return on capital and earnings yield. He also looks at three stocks that currently get high marks from his Greenblatt-based model, which is up more than 50% in 2013. Among them: Weight Watchers International.