The interest criteria are built by Facebook’s algorithms based on the activity of an audience over the past 30 days and on the global use of users, their interactions, their online activity (see: How Facebook determines knowledge of audiences). An audience defined by an interest criterion is thus distinguished by members of a Facebook page for several reasons:
the timing of an interest of an audience is based on the last 30 days
the notion of interest is assumed by Facebook’s algorithms but not declared through likes on a page,
the notion of interest is built starting from a global activity on Facebook’s looks but also through online activity.
There is thus not necessarily a correspondence between a Facebook fan page and a criterion of interest. Certains fan pages involving a large number of fans may not have an equivalent in terms of interest criteria and vice versa.