Usability

1
Usability

• Definition
• the capability in human functional terms to be
  used easily and effectively by the specified
  range of users, given specified training and user
  support. To fulfil the specified range of tasks
  within the specified range of environment
  scenarios.
• Dimensions
• effectiveness
• learnability
• flexibility
• attitude
• Usability criteria

2
User Needs Analysis
Designing for Usability
Conceptual Physical Design
Problem Defn.
Guidelines Standards
Analysis
Prototyping
UI Toolkits
Design
Analytic
Support Documentation
Implementation
Expert
Testing
Observational
Survey
Maintenance
Experimental
Evaluating Usability
3
Evaluation methods

• Analytic
• formal methods or semi-formal interface
  descriptions to predict user performance
• Expert
• human factors or interface design experts assess
  an interface
• Observational
• observe or monitor users behaviour
• Survey
• elicit users subjective opinions
• Experimental
• test hypothesis

4
Analytic evaluation

• Predictive
• requires task analysis and user profile
• Models
• single layer
• KLM
• multi-layer
• GOMS
• CCT
• CLG

5
Expert evaluation

• Expert walkthrough
• Cognitive walkthrough
• detect 50 usability problems?
• Heuristic evaluation
• 20-50 ?

6
Observational evaluation

• Direct observation
• Video recording
• Verbal protocols
• Think-aloud protocols
• Software logging

7
Survey evaluation

• Interviews
• structured
• flexible
• Questionnaires
• open/closed
• yes/no
• rank order
• multi-point
• semantic differential
• Likert

8
Experimental evaluation

• Test hypotheses
• Objective
• Requires careful planning
• Costly

9
Usability Metrics

• Performance metrics
• duration measures
• count measures
• proportion of task completed
• quality of output
• Measurable features
• time
• errors
• visual scanning patterns
• patterns of system use
• paths
• attitudes

10
Usability evaluations

• Users
• representative of intended user population
• numbers?
• Tasks
• distinguish between different levels of
  performance
• representative
• critical tasks
• Environments
• usability lab
• working environment

11
Selection of method

• A function of
• development stage of product
• type of task
• type of system
• type of users
• data required (quantitative/qualitative)
• funds available