WASHINGTON, DC: Over 10% of Americans internet users were active on the "microblogging" website Twitter in December 2008, a total rising to nearly one fifth of web users aged 18–34 years old, according to a study by Pew Internet & American Life Project.

As recently argued  on WARC Online by Isobar's Dan Calladine, "Tweeters" – the name for users of Twitter – are increasingly reshaping how events  are being reported online, and Mark Earls has also posited the view that the website offers an example of "herd" behaviour.

Some 9% of US web users had participated on Twitter in November last year, a total rising from 6% saying they had done so in May 2008, reflecting the rise of the portal in popular consciousness.

Usage levels reached 10% among of 35–44 year olds, a figure which halves among web users of 45–54 years of age, and reaches a low point of 2% among the over-65s.

Around 17% of households with an income of less than $30,000 (€23,617; £20,983) per year used the service in December, compared with 10% of those households earning over $75,000.

Pew also found the average age of Twitter users is 31, compared with 27 years old for MySpace, 26 for Facebook, and 41 for LinkedIn.

Data sourced from Marketing Charts; additional content by WARC staff