Set Usability Criteria

Use measurable usability criteria for the user interface to assess the likely success of the system during testing or user trials.

Consider the following usability criteria:

Ease of learning-How easy do users find it to learn to use the interface?
Efficiency once learned-How efficient are users after they are familiar with the interface? Their productivity should increase.
Ability of infrequent users to re-learn-How easy do occasional users find it to re-learn how to use the system after a break?
Good design features, such as keeping the number of menu levels low, should help. Keeping a record of recurring problems will also be helpful, possibly even using the system itself to record problems.
Frequency and seriousness of errors-How often do errors occur and how serious are they? Do any errors occur repeatedly?
Measure these criteria by counting and classifying the errors to give the number of errors as a percentage of the total number of times a procedure executed. This will help to balance error ratios for often and infrequently used procedures.
User satisfaction-How satisfied are the users?
This can be subjective, but it does help to gauge user acceptance of the interface. However, the speed with which new users take up the new system or facilities may provide some measurable indication of satisfaction.