A very good set of logitudinal data has been gathered
by University of Lethbridge Sociology professor Reginald Bibby. He has done
regular surveys of several thousand Canadians for thirty-five years with a
substantial fraction, about 50%, being repeated. He also recieved funding to do
two specific surveys of teenagers. He has a number of publications. The most
interesting concliusions he's reached is that secularization appears to have
slowed in Canada, although the level of atheism and agnosticism is at record
high levels. He talks about a la carte religious beliefs and non-institutional
spirituality.
And Canada's census asks religion questions and has
a 125 year data base of affiliation data. There are also periodic surveys and
special publications of the Statistics Canada agency that you would find
interesting, many available free online.
Because the fraction of persons with New Age or Pagan
beliefs is still tiny, well under a percent self-identify as such, it won't be
as good for your purposes, except that it will be an entire population.
In the United States, I really like the work of Helen A
Berger, whose substantial survey was cross-correlated with the General Social
Survey of the American population, so that more interesting comparisons can be
made. Berger "A Community of Witches - contemporary neo-Paganism and Witchcraft
in the United States" (ColumbiaC: U South Carolina Press, 1999); Berger, Evan A
Leach, Leigh S, Shaffer "Voices from the Pagan Census 0 A National Survey of
Witches and Neo-Pagans in the United States" (USC Press, 2003); Berger and
Douglas Ezzy "Teenage Witches - Magical Youth and the Search for the Self" (New
Brunswick NJ: Rutgers U Press, 2007); Berger ed. "Witchcraft and Magic
Contemporary North America" (Philadelphia: U Penn Pres, 2005).
Blesings of Klio,
Sam Wagar