Therin of Andor wrote:
The hardest parts of such statements are: how do you know the difference between casual and diehard fans (ie. during the height of TNG's popularity, a huge number of the general public admitted in polls to identifying as a "Star Trek fan" in that, yes, they watched it on TV regularly); what about fans who go back to a movie over and over and over?; and what about fans who borrow their friends' ST books and comics?
Although it has to be said, these kinds of numbers can be very closely approximated by the toolsets we have available in the context of, for example, a marketing research mix ("MR mix") - in general, a look at both secondary (existing) data and primary (as in: collected by or for the organization) data works best.
Of course, this is costly both in terms of time and money.