How to summarize fields with Value List selections?

[ratfile]

Using FMPro v8.5.

I'd like to create a summary field that counts the number of occurances of value list selections for a particular field. For ex. we have a field called "Activities", that can have 0+ checkboxes selected (rafting, riding, scenic flights, etc). I want to display on a report the number of boxes checked for the entire table for each of these categories (not by record, just totals).

For ex:
ACTIVITIES
Rafting 8
Riding 4
etc....

So far I cannot find a way to construct summary field(s) for this. How are the value list selections stored? Can they be parsed as plain text for regex matching?

thanks,
Bob