Since social media users have various purpose such as tightening friendship and obtaining information, it might be easier to model a user's interest and to provide personalized information if the user's purpose can be inferred. In this paper, we analyze the friendship of Twitter users and its effects on Twitter usage. According to our analysis, although the number of offline friends is smaller than that of online friends, a user more actively responds to the microblogs posted by the offline friends. We expect that our analysis is helpful to model a user's social behaviour and interest.
