Usability Metrics

Usability requirements are the metrics by which we judge that a product is easy enough to use. As I mentioned before (here and here), an ease of use requirement might specify:

• Profile. A typical user’s prerequisite skills and experience.
• Effort. A limit on the number of user gestures (keystrokes, mouse clicks, etc.) it should take to accomplish a functional task.
• Duration. A limit on the amount of time that it will take a typical user to perform the functional task.

Reading this post on the different skill levels of users, I realized I hadn't specified that product managers should generally apply this pattern to a range of users. User skill levels range on a continuum from novice to expert, and experience levels range from beginner to seasoned.

Ideally, the product manager addresses ease of use for the full continuum of skill and experience levels, but such metrics may not be realistic to formulate. It may suffice to specify metrics for a finite set of user levels, e.g.:

• novice
• competent
• expert

In my next entry, I will elaborate on the duration metric.