Number of GA PFL / number of GA PFL that end up going wrong and end up on the ground
Also a very small number, but just might be higher than the first answer.
Reminds me of the Meteor asymetric handling exercises in the 50's; they killed more pilots than actual engine failures. Here's an interesting stat that makes you think about how our attitudes to safety have changed. The RAF lost some 850 (yup, that's 850) Meteors with the loss of around 370 pilots.