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CISB213 Human Computer Interaction
Usability Engineering
1
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Learning Outcomes
At the end of this lecture, you should be able to:
Define the term UsabilityEngineering
Describe the various steps involved in UsabilityEngineering Lifecycle
Apply Usability Engineering Lifecycle in designing any
system or application
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Key Terms you must be able to use
Ifyou have mastered this topic, you should be able to use
the following terms correctly in your assignments and
exams:
Usability engineering Usability lifecycle
Usability goals
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Usability
Usability: the extent to which a product can be used by
specified users to achieve specified goals with effectiveness,
efficiency and satisfaction in a specified context of use.
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Usability
Why is usability important?
It makes the difference between performing a taskaccurately and completely or not, and enjoying theprocess or being frustrated.
Determine the success or failure of a system
Poor usability
Reduce productivity
Increase cost time and effort
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Usability usually refers to software but is relevant
to any product. Some ways to improve usability
include: shortening the time to accomplish tasks,
reducing the number of mistakes made,
reducing learning time,
and improving people's satisfaction with a system.
Usability
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According to Jakob Nielsen (2003), usability is defined by 5
quality components :
Learnability : ease of learning for novice users.
Efficiency : steady-state performance of expert users.
Memorability : ease of using system intermittently for casualusers.
Errors : error rate for minor and catastrophic errors.
Subjective Satisfaction : how pleasant the system is to use.
Usability
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Learning Curves
Some systems are designed to focus on learnability.
Others emphasise efficiency for proficient users.
Some support a combination of ease of learning and anexpertmode(for example rich menus and dialogues plus acommand/ scripting language)
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Domain & Expertise
ExtensiveComputer
Experience
Ignorant
A
boutthe
Domain
MinimalComputer
Experience
K
nowledg
e
ableAbou
t
t
heDomain
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Relationship between Usability Goals and User Types
Novice Users:No or limited knowledge of the occupational task tobe performed, and of computers and interfaceconcepts or
Knowledge of the occupational task to be performed,andof computers and interface concepts
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Relationship between Usability Goals and User Types
Knowledgeable Intermittent Users:Understanding of the task concepts
Broad knowledge of computers and interface
concepts.Intermittently use the system and may therefore haveproblems with retention
Expert Frequent (Power) Users:Thoroughly familiar with both task and interfaceconcepts. They are likely to use the system often andappreciate short cuts to speed their work.
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Typical Ways of Measuring Usability
Learnability: pick novice users of system, measure time to
perform certain tasks.
Distinguish between the various timings taken for some general
computer experience.
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Typical Ways of Measuring Usability
Efficiency : decide definition of expertise, get sample expert
users (which tends to be difficult), measure time taken to
perform typical tasks.
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Typical Ways of Measuring Usability
Memorability : get sample casual users (who are usually away
from system for certain time/duration) and measure time to
perform typical tasks.
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Typical Ways of Measuring Usability
Errors : count minor and catastrophic errors made by users while
performing some specified task.
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Typical Ways of Measuring Usability
Satisfaction : ask users subjective opinion (questionnaire,
interview), after trying system for real task.
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Usability Engineering
The term usability engineering describes a process of userinterface development, sometimes referred to as user centreddesign.
It is a lifecycle process that puts an early emphasis on userand task analysis and actual user involvement in the designand testing of a product.
A product developed with such a user centred process is likely
to be a more usable product than one that is developedindependent of user considerations and involvement.
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UsabilityEngineering Lifecycle
Parallel Design Sketches
Participatory Design
Iterative Design
Final Released Product
Users, Tasks,
Environment Analysis
Usability Goals , Competitive Analysis
First Prototype
Formative Testing
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1. Identify user requirements and problems
Profile Users
Task Analysis
2. Identify usability goals based on user requirements3. Checkout similar products
4. Design and prototype a solution (involve users)
5. Evaluate prototype
Usability testing (real users and real tasks)
6. Reiterate steps 4-5 until users are satisfied
Usability Engineering Lifecycle
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Identify user requirements and problems:
Define your user population.
Determine the distribution of skills, knowledge andexperience within your user population.
Assess the users skill level with respect to both thetask and computer domain.
Usability Engineering Lifecycle
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Identify user requirements and problems:
Typical Profile:
40 % Novice Users
57 % Knowledgeable/Intermittent Users
3 % Expert Users
Other Important Information:
10 % of user population colour blind
15 % are the elderly
Usability Engineering Lifecycle
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Identify user requirements and problems:
Task analysis allows a designer to identify the goals andpurposes of the intended user group.
This used to involve further analysis of userrequirements or investigation/observation of
customers
Used to guide user interface design
Usability Engineering Lifecycle
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Identify usability goals based
Learnability, Efficiency, Memorability, Error, Subjective
Satisfaction
Decide in advance on usability metrics and desired level of
measured usability
E.g.
Usability Engineering Lifecycle
Errors Per Hour
Optimal Target Current Unacceptable
0 1 - 3 4.5 > 5
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Check out similar products (Competitive Analysis)
Competitive analysis of software components
Competitive analysis of competing systems
Usability Engineering Lifecycle
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Parallel Design (Explore design alternatives)
designers should work independently, then compare draft
designs
Usability Engineering Lifecycle
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Participatory Design
Have access to pool of representative users.
Guided discussion of prototypes, paper mock-ups,screen designs with representative users.
E.g. Card Sorting
Usability Engineering Lifecycle
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Card Sorting - 1
Card sorting is a technique for exploring how people group
items, so that you can develop structures that maximize
the probability of users being able to find items
Is easy and cheap to conduct
Enables you to understand how realpeopleare likely
to group items
Identifies terminology that is likely to bemisunderstood.
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Card Sorting - 1
E.g. How would you group these tasks into 3 groups? (File, Edit,
View)
open, cut, normal view, close, copy, zoom in, save, paste, zoom
out, save, select, toolbar, print
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Card sorting is also a technique for allowing users actualselections out of several options to determine final designdecisions
Is easy and cheap to conduct Enables you to determine actual preferences versus
what users thinkthey prefer
Allows for more accurate understanding by user since
actual examples are seen
Card Sorting - 2
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Title
Content
Title
Content
Title
Content
Title
Content
Title
Content
Title
Content
Title
Content
Title
Content
A B C D
E F G H
Card Sorting - 2
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Applying Guidelines
Guidelines . . . general principles and advice about
usability characteristics of interfaces
Can be intimidatingoften hundreds or thousands of
specific recommendations.
Usability Engineering Lifecycle
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Prototyping & Testing
Perform usability evaluation as early as possible in the design
cycle by building and evaluating prototypes
Usability Engineering Lifecycle
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Learning Outcomes revisited
Check yourself to see if you can now:
Define the term Usability Engineering
Describe the various steps involved in Usability
Engineering Lifecycle
Apply Usability Engineering Lifecycle in designing any
system or application
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Q & A