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User Performance Metrics

by Kristoffer Bohmann, July 4, 2000

30 user performance metrics for informal usability evaluations.

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Most usability studies can be carried out using only two user performance metrics: However, alternative metrics are useful when reporting findings from qualitative usability evaluations. This list of measures identifies several alternative metrics. The metrics are intended to measure user performance only, while deliberately ignoring user satisfaction and design elements that are or are not visible to the user (e.g., placement of cursor).

Note also that user actions are not measured (e.g., number of commands to complete task). Such measures are seldom part of informal usability evaluations but may be used with formal usability evaluation methods emphasizing user keystrokes, critical paths, etc.

Task Time

  1. Time to complete a task
  2. Time to complete a set of tasks
  3. Time to complete a task after working with the system for 10 minutes (or two trials)
  4. First-time user time to complete task
  5. Repeat user time to complete task
  6. Percent of users completing a task in one minute or less
  7. Time to complete a task after one week away from the system
  8. Percent of task completed
  9. Percent of task completed per unit time
  10. First-time user time to perform a task
  11. Repeat user time to perform a task
  12. Time spent using help or documentation
  13. Task success rate
  14. Percent or number of completed tasks per unit time
  15. Number of tasks completed in 10 minutes

Task Error

  1. Number of (serious) errors per task
  2. Number of errors per unit of time / after 10 minutes
  3. Number of users making a particular error
  4. Number of users completing a task successfully (reverse metric)
  5. Ratio of task successes to failures
  6. Number of the user expresses frustration or dissatisfaction
  7. Number of novice/expert user errors in performing a task
  8. Number of errors per novice/expert user
  9. Number of novice/expert user with more than three errors
  10. Time to first user error
  11. Time spent understanding and correcting errors
  12. Number of requests for help or documentation
  13. Time spent using help or documentation
  14. Number of user who gave up a task
  15. Number of user errors after 10 minutes use
All metrics can be presented per task or set of tasks. Also, most metrics can be viewed per user, task, error, or unit of time. Time-constrained metrics may also be considered (e.g., number of errors after 2 minutes use).

References

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User Tasks in Ecommerce - 20 user tasks (not metrics) that can be used in usability evaluations

About the Author
Kristoffer Bohmann (biography) M.Sc. thinks and writes about high-quality user experiences. His philosophy: Users first. You can contact him at kristoffer@bohmann.dk.

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