David,
What do you mean by "regularly"?
- At least twice in the past 5 years?
- At least twice in the past 2 years?
- At least twice in the past 12 months?
- At least twice in the past 3 months?
- At least twice in the past week?
I say twice, because I assume that by "regularly" you mean at least more 
than once.  Then depending on how you define "regularly" you will get 
quite different answers. If you pick the first definition above, you 
will get a much bigger number than if you pick the last definition.
A slightly easier question to answer is, "How many people attend a 
contra dance on a particular night?" On any particular night, worldwide, 
there will be many regular dancers dancing, as well and some new people. 
A few regular dancers will not attend because they are sick, or vising 
relatives in Alberta.  The new dancers and the missing regular dancers 
may cancel each other out, at last to some degree.
So, the number of people dancing, worldwide, on a particular night might 
be a rough estimate of the number of regular dancers, worldwide. It may 
be a bit low if we pick a night when there are no dances in Denmark, or 
Oregon, but it would set a good lower bound.
So, how many people will be dancing, worldwide, on the the first 
Saturday in May, May 5th?
The members of these 2 lists probably have contacts with or attend 
nearly every regular dance in the world (and quite a few irregular ones, 
too). If everyone on these lists who attends a dance on May 5th would 
take a count and send both the name of the dance and the attendance to 
someone, a count of the total number of dancers at the known dances 
could be made.  It would take some work, as people would need to find a 
contact at dances they could not attend, but wanted to report. And the 
organizer who was doing the analysis would need to do enough planning 
ahead of time to be sure that as many dances, worldwide, were covered, 
as possible.
Rich Hart.
On 3/25/2012 1:31 PM, David Millstone wrote:
  [Duplicate posting to trad-dance-callers and
SharedWeight lists]
 A friend recently wrote me, "I am trying to pin down an unpindownable 
 number: namely the number of people in the world who regularly 
 contradance. Any idea of this number, or anyone who might steer me to 
 it?"
 I'm wondering if anyone on this list has tackled this question, has 
 developed even a crude methodology, and would be willing to share what 
 you came up with.
 As for "the world," with the exception of the folks in Denmark and in 
 England, I think we're really talking about the US and Canada in terms 
 of any significant numbers. I can ask friends ub Denmark for their 
 estimates. The annual country dance festival in Prague brings together 
 several hundred dance enthusiasts from central Europe, though their 
 definition of "regular" is certainly different from someone in the 
 Boston or SF Bay or DC areas.
 David Millstone