Three groups of internet users are mainly responsible for driving the growth of this activity: social network website users, those who connect to the internet via mobile devices and younger internet users (those under age 44).

Internet users who already use social network sites such as MySpace, Facebook or LinkedIn are also likely to use Twitter (35%), compared with just 6% of internet users who do not use such social network sites.

And, the more devices someone owns, the more likely they are to use Twitter or another service to update their status. Fully 39% of internet users with four or more internet-connected devices (such as a laptop, cell phone, game console or Kindle) use Twitter, compared with 28% of internet users with three devices, 19% of internet users with two devices and 10% of internet users with one device.

Survey data shows that internet users who use social network sites are more likely to use Twitter or another status updating service, independent of other factors such as that group's relative youth or propensity to go online via mobile

devices.

As of September 2009, 54% of internet users have a wireless connection to the internet via a laptop, cell phone, game console or other mobile device. Of those, 25% use Twitter or another similar service, up from 14% of wireless users in December 2008. By comparison, 8% of internet users who rely exclusively on tethered access use Twitter or another service, up from 6% in December 2008.

Analysis also shows that wireless access is an independent factor in predicting whether someone uses Twitter or another status update service. It is not simply because this group is likely to be young or tech-savvy. Owning and using a wireless internet device makes an internet user significantly more likely to tweet.

Age is another strong, independent predictor for use of Twitter and other status-updating services. Internet users ages 18 to 44 report rapid uptake of Twitter over the last nine months, whereas internet users ages 45 and older report slower adoption rates. For example, 37% of internet users ages 18 to 24 use Twitter or another service, up from 19% in December 2008.

The median age of a Twitter user is 31, which has remained stable over the past year. The median age for a MySpace user is now 26, down from 27 in May 2008, and the median age for LinkedIn is now 39, down from 40. Facebook, however, is graying a bit: the median age for this social network site is now 33, up from 26 in May 2008.

The report points out that Harvard Business School researchers analyzed a random sample of 300,000 Twitter accounts and found that "the top 10% of prolific Twitter users accounted for over 90% of tweets." In addition, says the report, Sysomos analyzed 11.5 million Twitter accounts and found that most people post just once per day (and one in five have never posted).

For now, concludes the report, "... it is clear that a 'social segment' of internet users is flocking to both social network sites and status-update services. This segment is likely to grow as ever more internet users adopt mobile devices as a primary means of going online.

For more about the study from Pew Research, please visit here.