Well, there are the public stats from tracking sites on raid participation. If you doubt those, we have the following confirmation from GC that raid participation (outside LFR) is down, and he doesn't think it's due to LFR stealing raiders.
waltteri wiikinkoski @pisuri
@Ghostcrawler Raiding in its current form has lost its niche among the players but i might be wrong. I mean from player participation %
Greg Street @Ghostcrawler
@pisuri Our numbers don't look very different. I am sure LFR stole some folks from 10s, but overall my suspicion is most didn't raid before.