Sherrilynne Starkie posted a link on Twitter this morning to an article on Twitter demographics. Written by Bill Tancer from Hitwise and featured in Time magazine this week, the article gives the results of research into Twitter user profile data.The research is interesting because (as Nick Burcher of Zed Media notes):
"There are a number of systems that allow analysis of what Twitter users are posting, but it is much harder to analyse who they are."
These are the key points about Twitter demographics from the Hitwise data:

• Males make up 63% of Twitterers
• California residents account for more than 57% of Twitter's visitors
• Twitter's largest age demographic is 35-to-44-year-olds who make up 25.9% of its users.
• 14.7% of Twitter visitors are type H03 a.k.a the "Stable Career," comprising a "collection of young and ethnically diverse singles living in big-city metros like Los Angeles, Philadelphia and Miami." The Stable Career tends to work in the arts and entertainment industry, drive small cars and espouse very liberal political views.
• 12.3% of Twitter's visitors are H01 a.k.a. the "Young Cosmopolitan," 40-somethings likely to drive a Prius, earn household incomes over $250,000 per year and also identify with very liberal politics.

It turns out that Twitter is not just 18-24 year olds using the service as a substitute for SMS texting (especially now Twitter has disabled certain SMS features). Older, professional audiences are key Twitter user demographics too, meaning that the service is more mainstream and more valuable (given the average spending power of users) than previously thought.

I also presume that the remaining 43% of Twitter users that don't reside in California must live in London or Brighton. Well, according to my Twitter stream anyway...