What is Usability Usability by paulj

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									               What is Usability?



                  Kyung-Sun (Sunny) Kim

                       Assistant Professor
                  School of Lib. & Info. Studies
                 University of Wisconsin-Madison

                    E-mail: kskim@slis.wisc.edu




                           Usability

• Extent to which a product can be used by
  specified users to achieve goals with
  effectiveness, efficiency and satisfaction
  in a specified context of use (ISO 9241)




            Usability in Perspective
• System acceptability
   Social acceptability
   Practical acceptability
     •   Cost
     •   Compatibility
     •   Reliability
     •   Usefulness
           – Utility
           – Usability:
                -- Easy to learn
                -- Efficient to use
                -- Easy to remember
                -- Few errors
                -- Subjectively pleasing           (Nielsen, 1994)




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                Usability Attributes

    • Learnability
    • Efficiency
    • Memorability
    • Errors
    • Satisfaction




                         Learnability
  • The most fundamental usability attribute
  • Test with novice users                                          -
     - Is it easy for novice users to learn to use the system?
  • Novices’ experience on the initial part of the learning curve


      Efficiency




                                            Time

             System designed for novice users




                          Efficiency
• A high level of productivity
• Test with experienced/expert users
   - How efficient is the system?
   - What is the maximum level of performance of the system?

• Experts’ steady-state level of performance



Efficiency




                                   Time




                                                                        2
                     Memorability
• Test with casual users (who are using a system
  intermittently, have some experience with the
  system)
• Can the user who has temporarily stopped using a
  system still remember an interface of the system?
• Relatively rarely tested
• Recognition > Recall




                            Errors

 • Errors: Any action that does not accomplish
    the desired goal
 • Fewer and less serious/catastrophic errors
      Simple errors:
        • Easily corrected
        • Resulted in longer performance time
      Catastrophic errors:
        • Not noticed by users, leading to faulty work product
        • Destructive, difficult to recover




         Subjective Satisfaction
• How pleasant it is to use the system (after the user
  had a chance to use the system)
• Important for systems used on a discretionary basis
  in a nonwork environment
• Different from public’s general attitude toward the
  system




                                                                 3
                   Usability Testing
  • The primary goal is to improve the usability of a
      product.
  • The participants represent real users.
  • The participants carry out real tasks.
  • You observe and record what participants say and
      do.
  • You analyze the data, diagnose the real problems,
      and recommend changes to fix those problems.
                                                (Dumas & Redish, 1999)




            Usability Evaluation Methods
  •   Heuristic evaluation (no user)
  •   Cognitive walkthrough (no user)
  •   Performance evaluation
  •   Thinking aloud (Verbalizing thoughts while using a system)
      [n=1]; Constructive interaction [n>1]
  •   Observations
  •   Questionnaires
  •   Interviews
  •   Focus groups
  •   Logging actual use
  • Retrospective testing (Retrospective thinking aloud)




            Usability Lab: Simple Setup

                                Camcorder




System to test                  Participant


                                          Observer




                                                             Test Room




                                                                         4
                    Usability Lab
Observation Room                          Test Room


        Monitor showing
        User’s screen


          Event logger



         Video editing,
          control


         Experimenter’s
          Workstation




     Acceptance of Usable System
  • People
  • System
  • Interaction between people & system
      Socio-technical
          Different settings/contexts
      Political
          Distribution of power




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