We expect one serious injury per evac and one fatality per two evacs.
I'm also surprised at the fatality figure. My guess would be that the stats take into account serious accidents where an evacuation has been initiated but where cause of death is something other than the evacuation itself (e.g. Manchester).
I'd be amazed if there is a fatality per 2 evacs if there is no fire in the cabin or fatal injuries sustained during impact.