Shackle (1991)
About Usability
Friday, June 15, 2012 Bi5 Agency Sondra L. Duckert Bachelor Thesis Exam E-Concept Development TEAM 3, Third Semester
Nielsen (2000)
Preece (1994)
Defining usability
Defines usability as:
Defines usability as:
Defines usability as:
The definition of usability is influenced by the experience of those who proposed the definitions and the domain in which they practiced usability. Common factors linking the definitions are the user, the task, the technology and the context of use.
"A system's capability in human functional terms to be used easily and effectively by the specified range of users, given specified training and support, to fulfill a specified range of task, within the specified range of environmental scenarios."
"A measure of the ease with which a system can be learned or used, its safety, effectiveness and efficiency, and the attitude of its users towards it."
"The engineering ideal of solving a problem for the consumer," and it aims to place "your customers' needs at the center of your Web strategy."(2000)
A Common Thread
Perceptions of Usability As a Quality Factor Model
Usability Attributes
Perceptions of Usability based on
Effectiveness
McCall Shackle
Efficiency
Satisfaction
Learnability
Operability
Communicativeness
Training
Effectiveness Flexibility
Subjectively Pleasing
Learnability
FURPS
Consistency
Human factors
Aesthetics
Online and context sensitive help Wizards and agents User documentation
Nielsen
Errors
Efficiency
Satisfaction
Learnability Memorability
Preece et al.
Effectiveness
Efficiency
Enjoyableness
Preece et al.
Flexibility
Efficiency Throughput
Attitude
ISO 9241-11
Effectiveness
Efficiency
Satisfaction
ISO 9126-1
Operability Usability Compliance
Donyaee et al.
Effectiveness Accessibility Universality Usefulness
Abran et al. Schneiderman et al.
Safety
Safety Learnability
Attractiveness
Understandability Learnability
Efficiency Productivity
Satisfaction Trustfulness
Learnability
Safety
Effectiveness
Efficiency
Satisfaction
Learnability
Security
Rate of errors by users
Speed of performance
Subjective Satisfaction
Time to learn Retention over time
Social acceptability
easy to learn
Usefulness Usability
cost compatibility
Practical acceptability
reliability
efficient to use
etc.
A model of attributes of system acceptability (Nielsen, 1993)
Image Source: Brian Fling
Usability together with utility are considered to influence the usefulness of the product. Usefulness is one of the attributes affecting acceptability. (Nielsen 1993)
speed
effectiveness
Usability
few errors subjectively pleasing
flexibility
attitude
easy to remember
errors
learnability time to learn
Acceptance
System acceptability
Utility
Utility
retention
Likeability Costs Product acceptance (Shackle 1991)
ISO 9241
About Usability
(1998)
Friday, June 15, 2012 Bi5 Agency Sondra L. Duckert Bachelor Thesis Exam E-Concept Development TEAM 3, Third Semester
ISO 25010
ISO 9126
(2011)
(2001)
Context of Use
Quality of Use
SQuaRE Model :
"Usability is the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and with satisfaction in a specified context of use."
"Usability is the capability of the software product to be understood, learned, used and attractive to the user, when used under specified conditions."
Product Quality and Quality in Use
'Usability is a property of the overall system: it is the quality of use in a context.'
"Usability can either be specified or measured as product quality characteristic in terms of its sub-characteristics, or specified or measured directly by measures that are a subset of quality in use."
Software Quality Factors for Evaluation
Usability and Quality intended objectives
ISO/IEC 9126-1
goals
users usability: extent to which goals are achieved with effectiveness, efficiency and satisfaction
task
ISO 9126-2 External Metrics
Sub-characteristics
ISO 9126-3 Internal Metrics
Characteristics Suitability
equipment
Maturity effectiveness
Accuracy
outcome of interaction
Fault Tolerance efficiency
Context of use
Security Recoverability
satisfaction
product
Functionality
Interoperability Compliance
Quality of use measures
Compliance
Usability framework
Reliability Analyzability
Quality ISO/IEC 9126
ISO 9241
Time behavior
Change-ability
Resource utilization
Stability
Compliance
Testability
Efficiency
Maintainability
Metrics
environment
Compliance Adaptability
Portability
ISO 25010
Install-ability
Understandability
Co-existance
Learn-ability
Replace-ability
Operability
Usability
Product Quality
Attractiveness
Compliance
Interoperability Co-existence
Compatibility Functional Su i ta b i l ity
Installability Replaceability Adaptability
Availability Maturity Recoverability
ISO 25010
Efficiency
Eff ect iv eness
Effi ciency
Fault tolerance
M aint a i n a b i l i t y
Testability
Time behavior Resource utilization Capacity
Effectiveness
Reliability
Reusability Modifiability
Quality in use
Po r ta bi l i t y
Modularity
Analyzability
Compliance
Functional completeness Functional correctness Functional appropriateness
Usability Per f o rm a n ce E f fi c i e n c y
Usefulness Trust Pleasure Comfort
ISO 25010 Sat isf act ion
Economic Risk Mitigation Health and Safety Risk Mitigation
Learnability Confidentiality Integrity Non-repudiation Accountability Authenticity
Appropriateness recognizability Operability
Sec urit y
User error protection User interface aesthetics Accessibility
Fre e d o m from risk
Context Coverage Context Completeness Flexibility
Environmental Risk Mitigation
About Usability
Guidelines
Friday, June 15, 2012 Bi5 Agency Sondra L. Duckert Bachelor Thesis Exam E-Concept Development TEAM 3, Third Semester
Goals
Metrics
'A Usability Framework for mobile Web sites: How usability attributes and metrics can help in optimizing mobile Web sites. A literature review.'
Attributes and Metrics
Usability Framework Foundation of a Usability Framework: A metric for evaluation, based on usability goals and guidelines. No.
Guidelines
Explanation The accuracy and completeness with which users achieve specified goals.
1
Accuracy
2
Response time
3
The system should be easy to learn and Ease of learning understand.
4
Task accomplish- The time it takes to complete a task successfully. ment Expectation
6
Attractiveness
The capability of the software product to be attractive to the user.
7
Error tolerant
Errors made by the user while completing a task.
8
Pleasure
The extent to which the functions that a system provides matches the needs of the user.
9
Trustfulness
10
Engaging
How satisfying is it for a user to interact with a system.
11
Features
Relevant system features are available.
12
Performance
The system performance relative to the amount of resources used under stated conditions.
13
Reading
The time it takes to read a text screen.
15
❖ ❖
The objective was to develop a set of metrics derived from a question format. This study used the Goal Question Metrics (GQM) method (Basil et al. 1994) for software quality improvement and measurements. The first step in the GQM approach is to identify the goal, then propose a set questions in how to achieve the goal and lastly use metrics to determine its value. The selected guidelines are accompanied by questions that will appraise each goal. The goal is then refined into several questions to ensure that they are measurable.
How difficult it would be complete a task.
Quality characteristics
Goal
Accuracy Effectiveness
The trust that a user has, in that the software will function properly.
Provide support/ The system should provide assistance to those that need additional help. Help User effort
❖
A system must respond promptly.
5
14
❖
Task accomplishment Features Efficiency Performance
Safety Satisfaction Attractiveness
Guidelines - No errors (few errors) - Successful completion of tasks - Accurate - Ease to input data - Ease of system usage - Support/help - Time response - Completed tasks - While using the system - Confidence in the system - User interface
The extent to which the software produces suitable results equal to the user investments.
Questions How many links completed without site abandonment? Does the site provide balance?
Metrics Time taken to learn each task
How accurate is the site information?
Measures
Guidelines Goals
How easy is it to input data? Is the site easy to learn? Are required fields highlighted?
Provide support/help Is the site flexible Number of errors Successful site browsing
Accuracy
The number of features
Effectiveness
The number of input actions Task Accomplishment
Features
Efficiency
Does the site provide support or help?
Amount of resources used
Does the site provide search filter options?
Site optimization (screen size)
Does the site provide local search functions? Does the website load quickly? How much interactivity is available on the site?
Performance
Time it takes to connect to a network Site response time Provide data protection
Rating scale for: Safety
Satisfaction
Are links safe for clicking? How do users perceive the website?
Attractiveness
Are privacy measures in place? Will users remember the aesthetics?
- Support - Input/output - Features - Interface - Site flexibility
Physical context
About Usability
Friday, June 15, 2012 Bi5 Agency Sondra L. Duckert Bachelor Thesis Exam E-Concept Development TEAM 3, Third Semester
Media context
Present location
Device of access
"Physical context will dictate how I access information and therefore how I derive value from it."
The media context isn't just about the immediacy of information we receive. It's about how we engage people in real time.
Modal context Modal Context Our present state of mind.
"Where should I eat" Should I buy it now or later? Is this safe or not? Excerpts from, Designing Mobile Experiences with Brian Fling (2009)
Context Matrix
Usability and Context 'Usability cannot exist without first defining the context of the system being tested.'
'How will users derive value from something they are currently doing?' What about 'mental models'? At-a-Glance Location-based Content-based Task-based Full Screen
Context social and organizational environment
task goals
physical environment technical environment
interaction
user
tasks
product
'Usability is a function of the context in which a product is used e.g. the users, task, technology and environment.' (Bevan 1994)
Satisfaction
Performance: Effectiveness & Efficiency
*Quality of Use measures *Quality of use measures determined by the Context of Use, ISO 9241-11 (Bevan, 1995)
Image Source: Brian Fling