Hi.
It is the accident rate per 100,000 flying hours. The comparison is apples-to-apples. The MD-11 is 7x more likely to crash than any recent Boeing/Airbus, and even MD/Douglas product, other than the -11.
I'm sure the accident rate for airplanes like the Comet and DC-4 and Ford Trimotor were higher.
cliff
LFW