The internet is widely considered the most measurable of advertising media, but those easily tracked click-throughs and e-commerce sales don’t tell the whole story. Far from it. Internet advertising stimulates off-line sales, too—in most cases, our firm finds that online campaigns increase sales more at advertisers’ retail cash registers than on their websites. Data like that should embolden executives to shift ever more dollars to online advertising.

A version of this article appeared in the April 2008 issue of Harvard Business Review.