Another part is the ability to marshall resources to capture these opportunity. That may take a perfect pitch, an eye for talents, or something else entirely.
so your definition of entrepreneur is probably a bit narrower than the usual definition... :-)
Also, the number of startups tends to rise during recessions could be interpreted the same way: the more people lose their regular jobs, the more entrepeneurs enter the rig. Talented or not, willingly or not... [1]
[1] http://www.wired.com/culture/culturereviews/magazine/17-06/n...
The difficulty of doing this in the field is trying to figure out what the appropriate methodologies to use are. It's not like it's easy to collect this information over time and ensure people are forthcoming (and in many regions where microfinance thrives, the poor are especially and legitimately suspicious of authority and people wanting personal information). Collecting information often becomes a messy process in collecting objective and comprehensive data.
My definition is simply someone who goes into business for themselves as opposed to getting a job. Taken that way, most people will be entrepreneurial given a good enough reason; and it's far from rare.
Also, it's surprising how many people work full time and have small side businesses they run part time. I believe I read a report that said the majority of US businesses are part-time, one-person only.