Here is a unique article on some usability metrics used to describe high level measurements:
“Usability metrics
Usability metrics are precise, quality measures used to evaluate the system. Their purpose is to produce a system that is neither under- nor over-engineered. To understand why usability metrics are useful, remember the joke about the guys out camping disturbed by a bear. As one of them puts on his trainers, the other says: “What are you doing, you’ll never outrun a bear!” The first one says: “I don’t need to outrun the bear. I just need to outrun you”. Usability metrics help you outrun the competition.
We recommend collecting usability metrics in the three Es: effectiveness, efficiency and emotion.
- Effectiveness
The accuracy and completeness with which users achieve specified goals. - Efficiency
The accuracy and completeness of goals achieved in relation to resources. - Satisfaction
Freedom from discomfort, and positive attitudes towards the use of the system.” (Userfocus, 2008)
UserFocus, Discount Usability: Time to push back the pendulum, Retrieved on December 14, 2008, from http://www.userfocus.co.uk/articles/discount.html