What makes a 'superfan'?

What is it that drives some people to be obsessed by certain bands or musicians?

The journalist Kate Mossman has been exploring the unique relationship between pop stars and their fans for a documentary on BBC Four called when 'When Pop Ruled My Life: The Fan's Story'.

Kate defined a superfan as someone who "met their band in the white heat of adolescence and possibly hasn't quite left that love yet".

Depeche Mode superfan Paul Gidley told Today he's "notched 42 concerts since '87". And follows "wherever my wife lets me go".