In 2012 a Microsoft employee working on Bing had an idea about changing the way the search engine di


In 2012 a Microsoft employee working on Bing had an idea about changing the way the search engine displayed ad headlines. Developing it wouldn’t require much effort—just a few days of an engineer’s time—but it was one of hundreds of ideas proposed, and the program managers deemed it a low priority. So it languished for more than six months, until an engineer, who saw that the cost of writing the code for it would be small, launched a simple online controlled experiment—an A/B test—to assess its impact. 

Within hours the new headline variation was producing abnormally high revenue, triggering a “too good to be true” alert. Usually, such alerts signal a bug, but not in this case. An analysis showed that the change had increased revenue by an astonishing 12%—which on an annual basis would come to more than $100 million in the United States alone—without hurting key user-experience metrics. It was the best revenue-generating idea in Bing’s history, but until the test its value was underappreciated.