It should be measured in terms of ALoSP (agree?), the people considering this issue are not producing this figure.
Why not? because it doesn't work?
AnFI - as I am sure you know, creating ALoSP requires a State Safety Plan including Safety Performance indicators to accurately produce data. This data needs to be based on a mandatory reporting system that highlights the required SPIs and therefore relies on operators being truthful about causes of incidents so that accurate data is recovered.
Imagine if someone, say, ran out of fuel and lost an aircraft (fortunately without loss of life) and then was untruthful about the cause of the fuel shortage (piss poor planning perhaps) - surely that person would be guilty of undermining the whole ASoLP process - just a hypothetical scenario but worthy of consideration.