Interesting. From the link:

"Those who 'do not belong' have first shed the practical and theoretical underpinnings of their religion, before finally overcoming social pressure to state 'your' religion. There are many who are not at the later stages of this secularisation process, so they still say they 'belong', although they are in the process of forgetting & discarding the physical and mental aspects of what they say they belong to. Sociologists know that if they count heads and ask about beliefs, more people say they belong to a religion, and say they have the beliefs of a particular religion, than actually do. People over-state their own religiosity; that's why statistics from polls will often give higher percentages of 'believers' than will head-counting and deeper investigations."