Ryan Sarver, Director of Platform at Twitter recently claimed that, according to the company’s data, 90% of active Twitters users use official Twitter apps on a monthly basis. Twitter defines “official apps” as applications it owns and operates for the Mac, iPad, Android and Windows Phone.

The data captured some attention because previous studies conducted by Sysomos suggested there were significantly more  users of non-official, third-party apps. For example, in a June 2009 report Sysomos found TweetDeck had nearly 20% of the client market.

Sysomos’ latest study may finally bring the matter to light, as the data shows only 58% of tweets come from official Twitter clients.

So, how to explain the gap between Twitter’s 90% claim and Sysomos’ data analysis that shows Twitter only has 58% market share? It’s simple, actually. Twitter’s analysis is based on the total number of users while Sysomos’ is based on the total number of tweets. It means there may be many official Twitter apps’ users who aren’t active users.

The most popular third-party apps were UberSocial, accounting for 16.4% of all tweets from non-official apps, followed by TweetDeck (13.1 %) and Echofone (9.2%).