Geoff,
Before we can get unscientific, three things need to be clearly defined
1. Knowledge
2. Understanding
3. Competency
4. Standard
Example. One of our pilots hurt himself badly doing something that he had been checked out on just 1 month prior. According to the ACP, he had no qualms writing him up as competent.
(ACPs are company examiners that are authorised to do the OPC equivalent (PPC) by Transport Canada)