How to measure vocal ability?

the four parameters for evaluating vocal ability are: 1) functional vocal fitness 2) vocal effort 3) vocal fatigue and 4) voice quality?

that vocal fatigue involves changes to vocal effort over a relatively short period of time?

Vocology: The Science and Practice of Voice Habilitation. Titze, I. & Abbott, K.Verdolini. The National Center for Voice and Speech. 2012.