For years Carrot Ink, a Dallas-based online retailer of printer cartridges, treated its Web site design like a guessing game: CEO John Howard says there was little way of knowing which design elements were drawing customers. But now Howard has removed the guesswork by paying a service to find out which elements of his site best drive sales. He uses a company that performs research called "A/B" or "multivariate" testing. This type of research was once available only through expensive software designed for large corporations. But now services are being offered over the Web for low monthly fees.

Howard designed home pages with different introductions - "Welcome to Carrot Ink," "Start Here," "Buy Ink for Less," or "Find Your Cartridge" - and different graphics. One showed a photo of carrots sprouting out of a printer, while another replaced the carrots with a dollar bill. Then the service randomly sent carrotink.com visitors to competing versions of the site. Howard found that the most successful combination - a headline of "Find Your Cartridge" and an image of a printer with carrots - led 18 percent more visitors to buy ink than his previous design had done.

The test took just 30 minutes for Howard to set up. "We do $6 million in annual sales," he says. "If I can get even a 1% increase in sales, [the testing service] pays for itself." -Julie Sloane