Steve....

Your link from folk18 is a bit disparaging about the MHM report.
The size and track record of MHM we can argue about but.....

These reports are based on an independent research study undertaken by Morris Hargreaves McIntyre. 4,294 adult festival goers completed short questionnaires at a range of six different folk festivals in England during July, August and September 2002. A further representative, weighted sample of 450 of these adults then completed long questionnaires during October 2002. A sample of these respondents then attended focus group discussions in December 2002. Market size data was calculated from attendance records gathered by the Association of Festival Organisers.........

looks like carefully constructed sampling and data collection to me.

Dave Eyre
www.collectorsfolk.co.uk