Does anyone know if there is an article on % of populations doing Pilates?

Off the top of my head, here are two main ideas:

First, check out the following (and I'm sure you'll find others...):

-IDEA may have some stats for you:)
-Stott Pilates
-there is a consumer magazine and website dedicated to pilates, something like Pilates life or Pilates today...
-Don't forget that pilates is a very specific niche/practice. Some of your stats might just relate to the overall population's need for an increase of regular physical activity (stressing the benefits and history of mind/body activities, like pilates)

Second:

To project the percentage of people who might attend your studio requires a more in-depth assessment of your geographic area and its demographics. For instance, is pilates already offered in rec centres, private studios?, etc..And if so, is there a demand for another studio? What would your studio offer that could justify it's establishment? Are people willing to pay extra for your service? Might you expand into home training (mat-based) or stick with strictly studio training? (mat and reformers) How long before you would show a profit?

I hope this helps even a little bit...

Best wishes,
Michelle