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Performance testing

Summary

Performance testing is a rigorous usability evaluation of a working system under realistic conditions to identify usability problems and to compare measures such as success rate, task time and user satisfaction with requirements.

Benefits

  • Major usability problems are identified that may not be revealed by less formal testing, including problems related to the specific skills and expectations of the users.
  • Measures can be obtained for the users' effectiveness, efficiency and satisfaction.

Method

Planning

  • It is important that the users, tasks and environment used for the test are representative of the intended context of use.
  • Select the most important tasks and user groups to be tested (e.g. the most frequent or the most critical).
  • Select users who are representative of each user group. 3-5 users are sufficient to identify problems. 8 or more users of each type are required for reliable measures.
  • Produce a task scenario and input data and write instructions for the user (tell the user what to achieve, not how to do it).
  • Plan sessions allowing time for giving instructions, running the test, answering a questionnaire, and a post-test interview.
  • Invite developers to observe the sessions if possible. An alternative is to videotape the sessions, and show developers edited clips of the usability problems.
  • Two administrators are normally required to share the activities of instructing and interviewing the user, operating video equipment (if used), noting problems, and speaking to any observers.
  • If possible use one room for testing, linked by video to another room for observation.
  • If usability measures are required, observe the user without making any comments.
  • If measures are not required, prompt the user to explain their interpretation of the contents of each screen and their reason for making choices.

Running sessions

  • Welcome the user, and give the task instructions.
  • Do not give any hints or assistance unless the user is unable to complete the task.
  • Observe the interaction and note any problems encountered.
  • Time each task.
  • At the end of the session, ask the user to complete a satisfaction questionnaire.
  • Interview the user to confirm they are representative of the intended user group, to gain general opinions, and to ask about specific problems encountered.
  • Assess the results of the task for accuracy and completeness.

Output

  • Produce a list of usability problems, categorised by importance (use post-it-notes to sort the problems), and an overview of the types of problems encountered.
  • Arrange a meeting with the project manager and developer to discuss whether and how each problem can be fixed.
  • If measures have been taken, summarise the results of the satisfaction questionnaire, task time and effectiveness (accuracy and completeness) measures.
  • If a full report is required, the offsiteCommon Industry Format provides a good structure.

More information

There is a detailed offsiteexample of a usability report using the Common Industry Format.

More information on usability testing can be found in the offsiteINUSE Handbook. The offsiteMUSiC Performance Measurement Method provides detailed instructions for measuring effectiveness, efficiency and satisfaction

STC offsiteresources for usability testing and usability labs.

Variations

Performance testing is used to obtain measures to establish or compare with usability requirements. Earlier in development less formal methods such as participatory evaluation or diagnostic evaluation are more appropriate.

Next steps

offsiteCollect feedback from users after release to inform any redesign. 

Case studies

Background reading

Dumas, JS, and Redish, Janice, A. (1999) Practical Guide to Usability Testing, Intellect Books.

Rubin, Jeffrey (1994) Handbook of Usability Testing. John Wiley and Sons, New York, NY

ISO 9241-11 Guidance on usability


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