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
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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
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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
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Usability Lab
Observation Room Monitor showing User’s screen Event logger Test Room
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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