Indeed, video streams at network TV sites were nearly two times more likely to be viewed by women ages 18-34 than men, who accounted for 22% and 12% of streams, respectively.

Whether CBS.com, NBC.com or ABC.com, visiting network sites shows a high level of brand devotion on the part of consumers, according to Michael Pond, a media analyst at Nielsen Online.

"Network Web sites are destinations for fans to deepen their experience," Pond said. "These viewers are very loyal and engaged and the Web site is a place to become immersed in the program."

Males, however, are still far more prone to be frequenting consumer-generated media sites like YouTube. For the top four CGM Web sites, streams were two-and-a-half times more likely to be viewed by men ages 18-34 than women--who accounted for 27% and 11% of streams, respectively, according to Nielsen's research, which combines its panel and server research methodologies.

"With shorter clips and a viral nature, CGM Web sites are much more about discovery, and consumers are likely to view content on more than one," Pond said.

Nielsen also discovered that online, prime TV watching is taking place during the day. Streaming activity at the top network TV Web sites over-indexed during the weekday lunchtime hours of 12 p.m.-2 p.m. By contrast, at CMG sites, the most popular time for viewing is during late-night hours on the weekend, between 11 p.m. and 6 a.m.

"Viewers take a break from work to catch up on the shows they enjoy," said Pond. "Prime-time visitors to network Web sites primarily enhance their TV viewing experience with features like online voting, Web-only promotions and other program-specific content."

Among network TV Web sites, Nielsen found relatively low viewer overlap, whereas among CGM Web sites, most viewers also watched video content on YouTube.

In December, Nielsen found 116.7 million unique viewers, or 73% of active Web users, watched approximately 6.2 billion video streams.

In this period, the average viewer spent nearly two hours and 10 minutes watching online video content, while each viewer watched nearly 54 video streams during the month.

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