Nick, if you're planning on using the results in a publication, you might want to define "active" or, more simply, leave out the word altogether. There are two reasons for that: (1) Different participants define "active" differently, which would decrease the validity of the results. For example, I thought "active" meant that one had posted in the thread and responded accordingly, whereas it's others who posted more than I classified themselves as non-active. (2) Defining the term would increase participation among those who are moderately active, who might hesitate to respond if they're unsure what category they fall into. You'd be surprised at how minor issues like this affect participation.
Of course, your primary interest may be in the lurkers, in which case the above isn't important.
ETA: Is there a reason you used revisionism for the pro side and denial for the anti? I doubt it will make a difference, but I'm curious.