Influential research firm Nielsen/NetRatings said Tuesday that it would begin to emphasize how long visitors spend on websites, rather than how many times they view a page, when comparing sites.
The move shook up website popularity rankings, favoring sites such as AOL, Yahoo and others that attract heavy users of e-mail and instant messaging over sites such as Google and Fox Interactive Media's MySpace.
The new form of measurement won't change where advertisers are putting their dollars online, said Debra Aho Williamson, a senior analyst with Internet research firm EMarketer Inc. But it might change the way websites are structured. For example, some newspapers spread out stories across multiple pages to increase page views, but they might have less incentive to do so under the new ranking system.
The two main Web measurement firms, Nielsen and ComScore Inc., are increasingly able to figure out exactly what people are looking at online, even when the page's content changes without having to hit the browser's refresh button. That means page views, once the industry standard, have become less important than some other metrics.
"We're maturing with the industry," said Scott Ross, Nielsen/Net Rating's director of product marketing.
Nielsen already counts page views, the amount of time a visitor spent on a page and the average number of times someone comes back to a particular site. But two recent major changes in Web publishing led Nielsen to favor the time-spent metric, Ross said.
First, technologies such as the software Ajax allow websites to show different parts of a page without refreshing the whole page. For instance, a visitor clicking "compose" on Yahoo's online e-mail service could write a new message without being shown an entirely new page.
The second shift that makes page views less relevant is the mainstream adoption of streaming video and audio, Ross said. A viewer would see the same page before and after pressing "play" on an online video -- only the images in the video player would change. And with websites that refresh sports scores automatically, a viewer could follow a whole baseball game without ever refreshing a page.
"We feel that minutes are better than page views for measuring the volume of usage on a site," Ross said.
Time Warner Inc.'s AOL rose to first in the new rankings. Its users collectively spent 25 billion minutes on the AOL Media Network in May, largely because of the popularity of AOL Instant Messenger.
The new measurement bumped Yahoo, the top-ranked Web brand for page views in May, to second place, with 19.6 billion minutes spent.
Fox Interactive Media, which includes the media darling MySpace, fell from second to fourth. But advertisers are likely to remain interested even if the site's ranking slides, Williamson said, because they know they can reach different types of audiences on MySpace or Facebook than they can on Yahoo or AOL.
"Smart marketers are going to look beyond the rankings," she said. "It's about how interested people are in spending time on the site."