2 million Twitter users

On January 6, 2008 I predicted that Twitter would reach 1 million users before April 1, 2008. The source for the number of Twitter users was (and still is) Twitdir. Twitdir finally reported 1 million Twitter users by the end of April. Twitdir announced that their was a flaw in their algorithm to count Twitter users, so the algorithm was changed. The backlog of Twitter users to be detected was caught up several weeks later. Yesterday evening I noticed that Twitdir reported just below 2 million Twitter users. Today the number reported exceeded 2 million.



The oldest Twitter accounts still active were created on March 21, 2006. It took Twitter over 550 days to get to 500,000 users (around the first half of October 2007). 150 days later (around mid March 2008), there were 1 million Twitter users. 50 days later (beginning of May 2008) there were already 1.5 million Twitter users. Another 50 days later Twitter had over 2 million Twitter users (end of June 2008). All these figures are based on the number of users reported by Twitdir.



The question of course is the reliability of the Twitdir figures. I performed a little test. Both Twitter and Twitdir offer the possibility to execute a location based search, returning both the number of Twitter users for a given location. I looked up the number of Twitter users reported by both sources for several locations.



For the 9 search arguments shown above, the number of Twitter users found by Twitdir is 20% to 30% lower than the number found by Twitter itself. It is likely that the number of Twitter reported by Twitter is also an underestmation of the real number. It is possible that there could be at this moment already over 2.5 million Twitter users. Who is capable of providing more insight on this issue ?