  A person's interests exist as an internal state and are difficult to define.
Since only external actions are observable, a proxy must be used that
represents someone's interests. Techniques like collaborative filtering,
behavioral targeting, and hashtag analysis implicitly model an individual's
interests. I argue that these models are limited to shallow, temporary
interests, which do not reflect people's deeper interests or passions. I
propose an alternative model of interests that takes advantage of a user's
social graph. The basic principle is that people only follow those that
interest them, so the social graph is an effective and robust proxy for
people's interests.
