• by Christine Champagne , April 29, 2011

Twitter cofounder Jack Dorsey, who recently returned to the five-year-old company in the role of executive chairman, has made it his mission to make Twitter more social - and he's got his work cut out for him.

The micro-blogging service is literally dominated by a tiny fraction of users, according to "Who Says What to Whom on Twitter," a study conducted by Cornell University and Yahoo Research. In fact, the study reveals 50 percent of tweets are generated by a mere 20,000 users.

You read that right. Less than .5 percent of Twitter's user base, which is made up of more than 200 million registered users, accounts for half of the tweets.

So who is this vocal minority? The "elite users"- as they're dubbed in the study (the rest are "ordinary users") - consist of four groups: media like CNN and The New York Times; celebrities such as Ashton Kutcher and Lady Gaga; organizations ranging from Starbucks to Twitter itself; and blogs, including Mashable and ProBlogger.

The elite users in the media camp are the most active - so much for social media sites like Twitter being the great equalizer when it comes to the dissemination of information. But celebrities have more followers, the study reveals.

Perhaps not surprisingly, the elite users aren't mixing with ordinary Twitter folk. Rather, the Twitter elite tend to stick together in a cliquish fashion, following each other, the study reports and it gets even more insular than that. Turns out celebrities follow other celebrities, media outlets follow other media outlets and guess who bloggers follow? Other bloggers.

The researchers behind "Who Says What to Whom on Twitter" arrived at these findings after studying tweets generated between July 28, 2009 and March 8, 2010. While five billion tweets were shared during that period, the researchers restricted their focus to 260 million tweets containing URLs