A range of methods can be used to assess usability:
"Usability" can be defined as the extent to which specified users can carry out specific tasks in particular environments with regard to effectiveness, efficiency, and user satisfaction. Effectiveness refers to the extent to which users can achieve task-related goals, efficiency refers to the cost of achieving these goals either in terms of time or some other resource. User satisfaction refers to the level of positive feeling engendered by the interaction and is measured by standard subjective assessment techniques. The aim of the usability tests will be to identify any usability problems and assess whether certain defined usability specifications have been achieved.
Heuristic evaluation involves relative 'experts' (computer-literate persons familiar with basic HCI) checking the different stages of interaction against a set of predefined heuristics, i.e. relevant usability principles.
The starting procedure for a cognitive walkthrough, as for most other types of evaluation method, is to define a small set of sample tasks which users might reasonably try to perform with the system, and which the system can support in its current state of development. The cognitive walkthrough entails moving step-by-step through each sample task, examining the potential for users to select the correct action at each step. In particular, the following four questions are asked for each action:
The aim of the user trials is to obtain a rich description of the types of problems encountered by sample users carrying out a series of standard tasks. User opinions can be collected by a structured questionnaire. Also their interaction with the system may be examined through analysis of the server log files.