You must first understand what 'interactivity' means. It's a slippery term taken to mean different things for example an online newspaper can be interactive because the audience can control what they see and hear by chosing the links or searching for specific stories. It is also interactive because a newspaper visitor can communicate with the producer of the newspaper blog/podcast/video footage and also debate topics with other visitors. The highest level of control would allow the visitor to be a contributor to the paper by submitting their own news packages for audience consumption. Sally McMillan states that interactivity can occur at many different levels and degrees of engagement and that it is important to differentiate between these levels.
‘If ‘interactivity’ is to move beyond its current status as a widely used but poorly conceptualized term, we must recognize that there are three fundamentally different types of interactivity. Scholars and others who use the term should indicate whether they are focusing on user-to-user, user-to-documents, or user-to-system interactivity or some combination of the three. ‘
McMillan, S.J. (2002). "Exploring Models of Interactivity from Multiple Research Traditions: Users, Documents, And Systems". in Lievrouw, L.; Livingston, S.. Handbook of New Media. London: Sage. pp. 162-182.