I believe statistics for various activities are available that have been calculated independently of venue, in other words, not necessarily within units of the National Park system. Years ago, I saw a show on PBS which discussed the various hazards of sundry outdoor activities. What stuck in my mind was that the accident rate for rock climbing was identical to the accident rate for driving in the automobile - a pretty good example of how we accept the hazards of a commonplace activity and emphasize the hazards of something exotic and unusual.

Sorry, I can't quote you a definitive source for the stats, but they are out there somewhere....