"Our experimental evidence reveals a rather more detailed and subtle picture: Significant portions of the Web cannot at all be reached from other significant portions of the Web," the researchers wrote. In many other cases, two Web pages can be bridged only by going through hundreds of clicks, they said.
If you picked two random pages and tried to click from one to the other, "there's a 75 percent chance that you will never get there," LaMore said.
If a path did exist, the average click separation would be 16, the researchers said. But if there were two-way links between the two sites -- in other words, if a path existed not only from page A to page B, but also from page B back to page A -- the number of average clicks would fall to about seven.
For e-commerce sites, the study underlined the importance of being on the Web's main thoroughfares, with links both to and from your site, rather than sitting at the end of the road, said Compaq spokeswoman Eileen Quinn.
For example, an "origination site" might have to increase its efforts to be easily found by Web crawlers. "That highly connected core of the Web is definitely where you want to be, versus some of those outlying areas," she said.
LaMore said the findings might also promote new strategies for Web surfing. Most people now use search engines to find particular sites or topics. But search engines such as AltaVista and Google also have the capability to search for pages that link to a specified page. So if you were interested in pets, you could look for all the sites that link to a particular online pet store.
Such tools could, in effect, reverse the Web's one-way traffic.
"The essence of surfing right now is one-way. ... If a browser were to have reverse-surfing capability, then you actually have more resources available to you than you do now," LaMore said. He also raised the possibility of cashing in on such links.
"If you know who's linked to you, then perhaps you know your content is valuable. (You might say) 'Hey, let's throw up a royalty, a fee for pointing to me,' " he said.
One of the researchers behind the earlier studies on the "19 clicks of separation" said he didn't dispute the new findings. Although he had not yet seen the full details of the new study, Notre Dame physicist Albert-Laszlo Barabasi acknowledged that his own work "used a poor man's method" to survey the Web.
"It's really good news that someone finally took the energy to map out the World Wide Web and look at its structure," Barabasi told MSNBC.com via telephone from Budapest, where he is on sabbatical.
He emphasised that his 19-click figure was an average, involving wide variation.
"The distance between Yahoo and everybody is about two or three. But take, for example, my Web page and try to find it without a search engine," he said half-jokingly. He said he would look forward to the study's formal presentation at the 9th International World Wide Web Conference in Amsterdam.
"I sentimentally believe in it, because the World Wide Web is what we call a directed network, in the sense that you can get from A to B, but you can't necessarily get from B to A," he said.
Like Barabasi's research, the new study found that Web interconnectedness followed the same sort of distribution found in organic systems -- and even in sociological networks. A classic example is Hollywood, where only a few at the top are part of the in-crowd and thousands at the bottom toil in obscurity.
"The Hollywood actor network has the same structure as the World Wide Web," Barabasi said.
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