Usability Metrics

To determine if a system meets user/human-centered design goals of effectiveness, efficiency, and user satisfaction, it is necessary to collect objective, quantifiable data.  The Human Factors Specialist develops experimental plans and data collection procedures to obtain and statistically analyze measures of usability.  Some of the most frequently used metrics for this purpose are listed by goal as follows:

• Effectiveness
  • Training time
  • Time to reach proficiency
  • Number of commands/actions per task
  • Number of commands/features that are never used
  • Number of times "help" is accessed
  • Success vs. failure rate in task completion

• Efficiency

  • Time to complete a task
  • Error rate
  • Number of tasks completed within a given time
  • Error recovery time
  • Decision time/delay

• User satisfaction

  • Positive vs. negative statements recorded during observations
  • Positive vs. negative questionnaire responses
  • Opinions expressed during interviews