Editing Usability (section)

====Metrics====
While conducting usability tests, designers must use usability metrics to identify what it is they are going to measure, or the usability metrics. These metrics are often variable, and change in conjunction with the scope and goals of the project. The number of subjects being tested can also affect usability metrics, as it is often easier to focus on specific demographics. Qualitative design phases, such as general usability (can the task be accomplished?), and user satisfaction are also typically done with smaller groups of subjects.<ref>Dumas, J.S. and Redish, J.C. (1999). ''A Practical Guide to Usability Testing'' (revised ed.), Bristol, U.K.: Intellect Books.</ref> Using inexpensive prototypes on small user groups provides more detailed information, because of the more interactive atmosphere, and the designer's ability to focus more on the individual user.

As the designs become more complex, the testing must become more formalized. Testing equipment will become more sophisticated and testing metrics become more quantitative. With a more refined prototype, designers often test effectiveness, efficiency, and subjective satisfaction, by asking the user to complete various tasks. These categories are measured by the percent that complete the task, how long it takes to complete the tasks, ratios of success to failure to complete the task, time spent on errors, the number of errors, rating scale of satisfactions, number of times user seems frustrated, etc.<ref>Kuniavsky, M. (2003). ''Observing the User Experience: A Practitioner's Guide to User Research'', San Francisco, CA: Morgan Kaufmann.</ref> Additional observations of the users give designers insight on navigation difficulties, controls, conceptual models, etc. The ultimate goal of analyzing these metrics is to find/create a prototype design that users like and use to successfully perform given tasks.<ref name=wickens>Wickens, C.D et al. (2004). ''An Introduction to Human Factors Engineering'' (2nd Ed), Pearson Education, Inc., Upper Saddle River, NJ : Prentice Hall.</ref> After conducting usability tests, it is important for a designer to record what was observed, in addition to why such behavior occurred and modify the model according to the results. Often it is quite difficult to distinguish the source of the design errors, and what the user did wrong. However, effective usability tests will not generate a solution to the problems, but provide modified design guidelines for continued testing.