Managements the world over are thanking their lucky stars there isn't a simple and reliable fatigue test, especially post mortem.
I was curious about this so I've asked him a follow-up question. Response:
"
One research study underway is measuring changes in the composition of saliva samples that accompany changes in fatigue level and how this correlates with human performance. The objective isn't to come up with a test/score which would say preclude pilots from flying due to "fatigue levels", rather it's part of a broader study to understand the effects of fatigue and its deleterious accumulation over time.
These particular salivary biomarkers are proving very good at predicting sleep deprivation and modelling the relationship between heart rate variability and levels of fatigue.
Of particular note, there's a well-established correlation between decreased cognitive performance during acute progressive fatigue arising from different concurrent stressors -- the very type of situation a pilot may encounter during an incident and be significantly and catastrophically impaired as a result.
I would argue that fatigue is now one of the greatest threats to modern aviation safety"
Hmm.