From the Overview of the Pew Internet & American Life Project Report, Twitter Update 2011 by Aaron Smith:
13% of online adults use the status update service Twitter, which represents a significant increase from the 8% of online adults who identified themselves as Twitter users in November 2010. 95% of Twitter users own a mobile phone, and half of these users access the service on their handheld device.
As in our previous research on Twitter use, African Americans and Latinos continue to have high rates of adoption of the service. Fully 25% of online African Americans use Twitter at least occasionally, with 11% doing so on a typical day.
Additionally, Twitter use by internet users ages 25-34 has doubled since late 2010 (from 9% to 19%) and usage by those ages 35-44 has also grown significantly (from 8% to 14%).
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