• by Mark Walsh  @markfwal, March 20, 2008

The share of traffic to question-and-answer Web sites has more than doubled over the last year, with Yahoo Answers drawing the vast majority of visits.

p> Even so, Yahoo has seen its market share in the category shrink to 74% from 94% as challengers including WikiAnswers, Answerbag and Askville chip away at the Web portal's dominance, according to new data from Hitwise.

Coming closest to Yahoo is WikiAnswers, an offshoot of Answers.com, with just over 18% market share, followed by Answerbag, at 4.5%. Amazon.com's Askville, meanwhile, claimed less than 1% of Q&A traffic.

But Q&A sites are benefiting generally from expanding consumer participation. "As we see user-generated content proliferating in different flavors, this is yet another way people are interacting with social media," said Heather Dougherty, research director at Hitwise.

The rise of "social knowledge" online is premised on people seeking answers and advice across a wide pool of volunteer experts and enthusiasts. The Q&A sites are harnessing the Web to tap into the so-called wisdom of crowds.

Growing interest in the category was reflected recently in speculation online that Ask.com might shift focus from search to a more Q&A-oriented service.

Ask.com would have a long way to go to catch up with Yahoo Answers, which had monthly traffic of 25.3 million in February, according to comScore Media Metrix. That's up from 17.4 million a year ago.

Yahoo Answers was also tops in average time spent at more than nine minutes per session, according to Hitwise. People spent only about half as much time on WikiAnswers at 4 minutes, 17 seconds, followed by Answerbag, with 3 minutes, 31 seconds.

As the largest Web portal, Yahoo has a built-in advantage in building up a Q&A property. In the face of declining market share, "they could try to funnel traffic from some of their other properties to build awareness and generate more traffic," said Dougherty. As one of its few successful forays into social media, Yahoo regularly touts Yahoo Answers as a key Web 2.0 property.

Among the top Q&A sites, Askville had the highest amount of new traffic, with 93%, compared to 52% for Yahoo Answers.