Twitter may have over 200 million registered users, but half of the tweets shared on the popular microblogging site are actually generated by a small group of "elite" members, a new study has found.

Researhers at Internet search engine Yahoo! who looked at about 260 million tweets posted on Twitter between July 28, 2009 and March 8, 2010 found that 50 per cent of the tweets -- or 140-character messages -- are shared by only a group of 20,000 users of the networking site, the Telegraph reported.

By using Twitter 'lists', the researchers were able to distinguish between elite users -- specifically celebrities, bloggers, and representatives of media outlets and other formal organisations -- and ordinary users.

"Based on this classification, we find a striking concentration of attention on Twitter -- roughly 50 per cent of tweets consumed are generated by just 20,000 elite users -- where the media produces the most information, but celebrities are the most followed," a Yahoo! researcher said.

"Information flows have not become egalitarian by any means," the researcher added.

The team also found that individuals on Twitter follow back far less than they're followed, making it a less "social" platform than the likes of Facebook.

"The Twitter follower graph, in other words, does not conform to the usual characteristics of social networks, which exhibit much higher reciprocity and far less skewed degree distributions, but instead resembles more the mixture of one-way mass communications and reciprocated interpersonal communications," they explained.

Earlier this month Twitter turned five and revealed that one billion tweets are sent a week, with an average of 140 million being sent a day.

Though the site has over 200 million accounts, it has not revealed how many of those are active.