Title: User Interface Design
1User Interface Design
- Southern Methodist University
- CSE 8316
- Spring 2003
2Temporal Relations and Usability Specifications
3Introduction
- Previous chapter discussed low level primitives
- Now focus on abstraction and relative timing of
events - Such issues as interruptibility and
interleavability should be part of interaction
design and not driven by constructional design.
4Introduction
- UAN can be used to specify
- Sequence
- Iteration
- Optionality
- Repeating choice
- Order independence
- Interruptibility
- Interleavability
- Concurrency
- Waiting
5Sequencing and Grouping
- Sequence
- Sequence One task is performed in its entirety
before the next task is begun - Represent in the UAN by grouping (horizontally or
vertically) without any intervening operators - Grouping
- Tasks can be grouped together using various
operators to form new tasks - Definition is similar to that for regular
expressions
6Abstraction
- Have only seen UAN describing articulatory
actions -- primitive tasks performed by the user.
- In this form, describing an entire interaction
design would be overly complex and difficult - Introduce abstraction by allowing groups of tasks
to be named. - As with procedures, a reference to the name is
equivalent to performing all the tasks described
by that name
7Abstraction
- To aid in reusability, allow tasks references to
be parameterized - Reusing tasks promotes logical decomposition,
providing for consistent system model - Abstraction hides details, but also hides user
feedback. This information can be listed at one
or both levels. - With task naming, can now perform top-down
design.
8Task Operators
- Choice
- Simple choice is represented in UAN with the
vertical bar, '. - Repeating choice is formed by adding the
iterators ' and '.
9Task Operators
- Order Independence
- Set of tasks that must be completed before
continuing, but order of completion of the
subtasks is not important. - Represented by the '.
10Task Operators
- Interruption
- Interruption occurs when one task is suspended
while another task is started - Since UAN describes what can happen, you cannot
specify an interruption, but rather what can be
interrupted (interruptibility) - To specify that A can interrupt B use A --gt B.
11Task Operators
- Uninterruptible Tasks
- Assume all primitive actions are uninterruptible
(e.g. pressing a mouse button). - Specify the uninterruptibilty of higher-level
tasks (e.g. modality) by enclosing in brackets,
ltAgt'.
12Task Operators
- Interleavability
- If two tasks can interrupt each other, they are
considered interleavable. - Assume that operator is transitive.
- Represented with double arrow, A lt--gt B.
13Task Operators
- Concurrency
- If two tasks can be performed in parallel (e.g.
two different users), then tasks are concurrent
Represented with '.
14Task Operators
- Intervals and Waiting
- Can add explicit time intervals between two
events. - Two forms
- If task B must be completed within n seconds of
task A A (tltn) B' - If task B is to occur only n seconds after task
A A (tgtn) B'
15Other Representations
- Screen Pictures and Scenarios
- UAN describes user actions, but does not describe
the format/display of screens - Should supplement UAN with screen layouts and
scenarios. - State Transition Diagrams
- Typical interface contains various states
- To provided global view of how states are
related, add state transition diagram to UAN
16Design Rationale
- Basic role of UAN is communication
- Important to provide reasons behind various
decisions - Gives motivation and goals and helps prevent
later duplication of mistakes
17Usability Specifications
18Usability Specifications
- Quantitative, measurable goals for knowing when
the interface is good enough - Often overlooked, but provide insurance that
multiple iterations are converging - For this reason, should be established early
19Usability Specification Table
- Convenient method for indicating parameters
- Contains following information
- Usability Attribute
- Measuring Instrument
- Value to be Measured
- Current Level
- Worst Acceptable Level
- Planned Target Level
- Best Possible Level
- Observed Results
20Usability Attribute
- Represents the usability characteristic being
measured - Must determine classes of intended users
- For each class determine realistic set of tasks
- Goal is to determine what user performance will
be acceptable
21Usability Attributes
- Typical attributes include
- Initial Performance User's performance during
the first few uses. - Long-term Performance User's performance after
extended use of the product - Learnability How quickly the user learns the
system - Retainability How quickly does the knowledge of
how to use the system dissipate
22Usability Attributes
- Advanced Feature Usage Usability of
sophisticated features - First Impression Subjective user feelings at
first glance - Long-term User Satisfaction User's opinion after
extended use
23Measuring Instrument
- Method to find a value for a usability attribute
- Quantitative, but may be objective or subjective
- Objective based on user task performance
- Subjective deal with user opinion
(questionnaires) - Both types are needed to effectively evaluate
24Benchmark Tasks
- User is asked to perform a task using the
interface - Most common objective measure
- Task should be a specific, single interface
feature - Description should be clearly worded without
describing how to do it
25Questionnaire
- Quantitative measure for subjective feelings
- Creating survey that provides useful data is not
trivial - Recommend use of scientifically created question
(e.g. QUIS)
26Values To Be Measured
- The data value metric
- Typically metrics are
- Time for task completion
- Number of errors
- Average scores/ratings on questionnaire
- Percentage of task completed in a given time
- Ratio of successes to failures
- Time spent in errors and recovery
27Values To Be Measured
- Number of commands/actions used to perform task
- Frequency of help/documentation use
- Number of repetitions of failed commands
- Number of available commands not invoked
- Number of times user expresses frustration or
satisfaction
28Setting Levels
- Having determined what and how to measured, need
to set acceptable levels - These levels will be used to determine when the
interface has reached the appropriate level of
usability - Important to be specific enough so that levels
can be reasonably set
29Current Level
- Present level of the value to be measured
- Values can be determined from manual system,
current automated system or prototypes - Proof that usability attribute can be measured
- Baseline against which new system will be judged
30Worst Acceptable Level
- Lowest acceptable level of user performance
- This level must be attained for the product to be
considered complete - Not a prediction of how the user will perform,
but rather the worst performance that is
considered acceptable
31Worst Acceptable Level
- Tendency/pressure is to set the values too low
- Good rule of thumb is to set them at or near the
current levels
32Planned Target Level
- The level of unquestioned usability, the ideal
situation - Serve to focus attention on those aspects needing
the most work (now or later) - May be based on competitive systems
33Best Possible Level
- State-of-the-art upper limit
- Provides goals for next versions
- Gives indication of improvement that is possible
- Frequently determined by having measuring expert
user
34Observed Results
- Actual values obtained from user testing
- Provides quick comparison with projected levels
35Setting Levels
- There are various methods for estimating the
levels - Existing systems or previous versions of new
system - Competitive systems
- Performing task manually
- Developer performing with prototype
- Marketing input based on observations of user
performance on existing systems
36Setting Levels
- The context of the task is important in
determining these levels
37Example usability table
Usability attribute Measuring instrument Value to be measured Current level Worst acceptable level Planned target level Best possible level Observed results
Advanced feature usage Add repeating appointment task per benchmark 3 Length of time to add a weekly appointment every week for one year after one hour of use 13 minutes (manually) 2 minutes 1 minute 30 seconds
38Example usability table
Usability attribute Measuring instrument Value to be measured Current level Worst acceptable level Planned target level Best possible level Observed results
First impression User reaction Number of negative/positive remarks during the session ?? 10 negative/2 positive 5 negative/5 positive 2 negative/10 positive
39Example usability table
Usability attribute Measuring instrument Value to be measured Current level Worst acceptable level Planned target level Best possible level Observed results
Learnability Add appointment task per benchmark 5 Length of time to successfully add appointment after one hour of use 15 seconds (manually) 15 seconds 12 seconds 8 seconds
40Cautions
- Each usability attribute should be
(realistically) measurable - User classes need to be clearly specified
- The number of attributes to be measured should be
reasonable. Start small and add as experience
grows - All project members should agree on the values
41Cautions
- The values should be reasonable
- If found to be too low, then increase them on
next iteration - If they appear too high, it may be they were not
realistically set or that the interface needs a
lot of work! Judgement call
42Expert Reviews, Usability Testing, Surveys, and
Continuing Assessment
43Introduction
- Designers can become so entranced with their
creations that they may fail to evaluate them
adequately - Experienced designers have attained the wisdom
and humility to know that extensive testing is a
necessity
44Introduction
- The determinants of the evaluation plan include
- stage of design (early, middle, late)
- novelty of project (well defined vs. exploratory)
- number of expected users
- criticality of the interface (life-critical
medical system vs. museum exhibit support)
45Introduction
- costs of product and finances allocated for
testing - time available
- experience of the design and evaluation team
46Introduction
- The range of evaluation plans might be from an
ambitious two-year test to a few days test. - The range of costs might be from 10 of a project
down to 1.
47Expert Reviews
- While informal demos to colleagues or customers
can provide some useful feedback, more formal
expert reviews have proven to be effective. - Expert reviews entail one-half day to one week
effort, although a lengthy training period may
sometimes be required to explain the task domain
or operational procedures.
48Expert Reviews
- There are a variety of expert review methods to
chose from - Heuristic evaluation
- Guidelines review
- Consistency inspection
- Cognitive walkthrough
- Formal usability inspection
49Expert Reviews
- Expert reviews can be scheduled at several points
in the development process when experts are
available and when the design team is ready for
feedback. - Different experts tend to find different problems
in an interface, so 3-5 expert reviewers can be
highly productive, as can complementary usability
testing.
50Expert Reviews
- The dangers with expert reviews are that the
experts may not have an adequate understanding of
the task domain or user communities.
51Expert Reviews
- To strengthen the possibility of successful
expert reviews it helps to chose knowledgeable
experts who are familiar with the project
situation and who have a longer term relationship
with the organization. - Moreover, even experienced expert reviewers have
great difficulty knowing how typical users,
especially first-time users will really behave.
52Usability Testing and Laboratories
- The emergence of usability testing and
laboratories since the early 1980s is an
indicator of the profound shift in attention to
user needs. - The remarkable surprise was that usability
testing not only sped up many projects but that
it produced dramatic cost savings.
53Usability Testing and Laboratories
- The movement towards usability testing stimulated
the construction of usability laboratories.
54Usability Testing and Laboratories
- A typical modest usability lab would have two 10
by 10 foot areas, one for the participants to do
their work and another, separated by a
half-silvered mirror, for the testers and
observers (designers, managers, and customers).
55Usability Lab (Interface Analysis Associates)
56Usability Lab (Interface Analysis Associates)
57Usability Testing and Laboratories
- Participants should be chosen to represent the
intended user communities, with attention to
background in computing, experience with the
task, motivation, education, and ability with the
natural language used in the interface.
58Usability Testing and Laboratories
- Participation should always be voluntary, and
informed consent should be obtained. Professional
practice is to ask all subjects to read and sign
a statement like this one - I have freely volunteered to participate in this
experiment. - I have been informed in advance what my task(s)
will be and what procedures will be followed.
59Usability Testing and Laboratories
- I have been given the opportunity to ask
questions, and have had my questions answered to
my satisfaction. - I am aware that I have the right to withdraw
consent and to discontinue participation at any
time, without prejudice to my future treatment. - My signature below may be taken as affirmation of
all the above statements it was given prior to
my participation in this study.
60Usability Testing and Laboratories
- Videotaping participants performing tasks is
often valuable for later review and for showing
designers or managers the problems that users
encounter. - Field tests attempt to put new interfaces to work
in realistic environments for a fixed trial period
61Nomos Lab
An observer's view of a test being carried out in
the purposely designed Nomos lab.
62Nomos Lab
Two sides of the one-way glass - actions and
problems are logged while the user carrys out
real tasks with the product.
63Usability Testing and Laboratories
- Field tests can be made more fruitful if logging
software is used to capture error, command, and
help frequencies plus productivity measures
64Usability Testing and Laboratories
- Game designers pioneered the can-you-break-this
approach to usability testing - providing energetic teenagers with the challenge
of trying to beat new games - This is a destructive testing approach
- users try to find fatal flaws in the system, or
otherwise to destroy it - has been used in other projects and should be
considered seriously
65Usability Testing and Laboratories
- Usability testing does have at least two serious
limitations - it emphasizes first-time usage
- has limited coverage of the interface features.
- These and other concerns have led design teams to
supplement usability testing with the varied
forms of expert reviews.
66Siemens Usability Lab
A control deck (shown above) allows the team to
witness users reacting to software as they
navigate the interface and attempt to perform
normal tasks. Separate cameras record facial
expressions and comments, use of manuals,
and activity on the screen itself. As a rule,
every session is recorded and held for later
review and analysis.
67Siemens Usability Lab
This section of the Siemens Center has been
arranged so the software design team can view
every move the user makes, interact with him or
her when necessary, and generally see and feel
their own design through the user's experience.
68Inventory of Facilities - U of Indiana
- 2 Sony DXC-107A CCD Color Video Cameras, equipped
with Canon R-II electrically controlled zoom
lenses and wall-mounted on Pelco remote-control
pan/tilt bases. All camera functions are remotely
controlled from the observation room by Pelco
MPTAZ Pan/Tilt and Scanner controls. - 2 Microphones 1 Audio-Technical
superhypercardioid (super shotgun) type for
discrete data collection and a cardioid
microphone for narration and overdubbing. - 1 Teac TASCAM M-06 six channel professional audio
mixer, monitored via 5W self-amplified speakers
or headphones. - 2 Scan converters 1 Extron Super Emotia high
resolution scan converter for capturing live
video from the subject's computer screen, and 1
Mediator medium-resolution scan converter for
titling and effects generation. - 2 Macintosh PowerMac 7500/100 workstations with
1710AV 17" monitors 1 located in the testing
room for use in evaluating Macintosh software,
and 1 located in the observation room for data
analysis, effects generation, and web-server
functions. Both machines feature video capture
and output (via scan converter) capabilities, and
are networked onto both the local LAN (Novell
ipx/spx) and Internet (TCP/IP). - 1 Dell XPS-90 Workstation with Dell 17"
multiscanning monitor, located in the testing
room for use in evaluating PC-compatible
software. This machine is also networked onto
both the local LAN (Novell ipx/spx) and Internet
(TCP/IP). - 1 Sony PVM-411 video monitor rack for monitoring
all online video sources. - 3 JVC BRS-800U industrial video cassette
recorders, equipped with SA-R50U time code
generator/reader boards and SA-K26U RS-422
interface boards 2 for capturing camera output
and 1 for capturing scan convertor (computer
screen) output. Each can function independently
or can be slaved to a single universal RMG-30U
serial remote control.
69Inventory of Facilities - U of Indiana
- 3 JVC TM-131SU Color Video Monitors located in
the observation room for monitoring online
sources during the evaluation session and
providing high-quality output for post-session
analysis and mixdown. - 1 JVC RMG-800U Editing Control Unit for
post-production assemble/insert mixdown of
recorded video source into condensed "highlights"
tapes. - 1 Panasonic WAV7 Digital Effects Generator/Mixer
for creating a variety of online and
post-production video effects including wipes,
fades, cuts, strobes, keys, mosaics, split-screen
and picture-in-picture effects. - 1 Optimus SCT-53 "Pro Series" dual audio cassette
deck with auto-reverse, dual digital time
counters, and high speed dubbing capabilities. - Speakerphone equipped with a flashing silent
ringer and a digital voicemail box. - Requisite cabling, stands, tables and other
paraphernalia to allow above equipment to
function and be used properly.
70Surveys
- Written user surveys are a familiar, inexpensive
and generally acceptable companion for usability
tests and expert reviews. - The keys to successful surveys are clear goals in
advance and then development of focused items
that help attain the goals.
71Surveys
- Survey goals can be tied to the components of the
Objects and Action Interface model of interface
design. Users could be asked for their subjective
impressions about specific aspects of the
interface such as the representation of - task domain objects and actions
- syntax of inputs and design of displays.
72Surveys
- Other goals would be to ascertain
- users background (age, gender, origins,
education, income) - experience with computers (specific applications
or software packages, length of time, depth of
knowledge) - job responsibilities (decision-making influence,
managerial roles, motivation) - personality style (introvert vs. extrovert, risk
taking vs. risk aversive, early vs. late adopter,
systematic vs. opportunistic)
73Surveys
- reasons for not using an interface (inadequate
services, too complex, too slow) - familiarity with features (printing, macros,
shortcuts, tutorials) - their feeling state after using an interface
(confused vs. clear, frustrated vs. in-control,
bored vs. excited).
74Surveys
- Online surveys avoid the cost of printing and the
extra effort needed for distribution and
collection of paper forms. - Many people prefer to answer a brief survey
displayed on a screen, instead of filling in and
returning a printed form, although there is a
potential bias in the sample.
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79Summary
- Extensive testing is a necessity
- Formal expert reviews have proven to be effective
- Must have an adequate understanding of the task
domain and user communities - Usability testing speeds up project TTM and
produces dramatic cost savings
80Product Evaluations
81Evaluation During Active Use
- A carefully designed and thoroughly tested system
is a wonderful asset, but successful active use
requires constant attention from dedicated
managers, user-services personnel, and
maintenance staff. - Perfection is not attainable, but percentage
improvements are possible and are worth pursuing.
82Evaluation During Active Use
83Evaluation During Active Use
- Interviews and focus group discussions
- Interviews with individual users can be
productive because the interviewer can pursue
specific issues of concern. - After a series of individual discussions, group
discussions are valuable to ascertain the
universality of comments.
84Evaluation During Active Use
- Continuous user-performance data logging
- The software architecture should make it easy for
system managers to collect data about the
patterns of system usage, speed of user
performance, rate of errors, or frequency of
request for online assistance. - A major benefit of usage-frequency data is the
guidance they provide to system maintainers in
optimizing performance and reducing costs for all
participants.
85Evaluation During Active Use
- Online or telephone consultants
- Online or telephone consultants are an extremely
effective and personal way to provide assistance
to users who are experiencing difficulties. - Many users feel reassured if they know there is a
human being to whom they can turn when problems
arise.
86Evaluation During Active Use
- On some network systems, the consultants can
monitor the user's computer and see the same
displays that the user sees while maintaining
telephone voice contact. - This service can be extremely reassuring the
users know that someone can walk them through the
correct sequence of screens to complete their
tasks.
87Evaluation During Active Use
- Online suggestion box or trouble reporting
- Electronic mail can be employed to allow users to
send messages to the maintainers or designers. - Such an online suggestion box encourages some
users to make productive comments, since writing
a letter may be seen as requiring too much effort.
88Evaluation During Active Use
- Online bulletin board or newsgroup
- Many interface designers offer users an
electronic bulletin board or newsgroups to permit
posting of open messages and questions. - Bulletin-board software systems usually offer a
list of item headlines, allowing users the
opportunity to select items for display. - New items can be added by anyone, but usually
someone monitors the bulletin board to ensure
that offensive, useless, or repetitious items are
removed.
89Evaluation During Active Use
- User newsletters and conferences
- Newsletters that provide information about novel
interface facilities, suggestions for improved
productivity, requests for assistance, case
studies of successful applications, or stories
about individual users can promote user
satisfaction and greater knowledge.
90Evaluation During Active Use
- Printed newsletters are more traditional and have
the advantage that they can be carried away from
the workstation. - Online newsletters are less expensive and more
rapidly disseminated - Conferences allow workers to exchange experiences
with colleagues, promote novel approaches,
stimulate greater dedication, encourage higher
productivity, and develop a deeper relationship
of trust.
91Controlled Psychologically-oriented Experiments
- Scientific and engineering progress is often
stimulated by improved techniques for precise
measurement. - Rapid progress in the designs of interfaces will
be stimulated as researchers and practitioners
evolve suitable human-performance measures and
techniques.
92Controlled Psychologically-oriented Experiments
- The outline of the scientific method as applied
to human-computer interaction might comprise
these tasks - Deal with a practical problem and consider the
theoretical framework - State a lucid and testable hypothesis
- Identify a small number of independent variables
that are to be manipulated - Carefully choose the dependent variables that
will be measured
93Controlled Psychologically-oriented Experiments
- Judiciously select subjects and carefully or
randomly assign subjects to groups - Control for biasing factors (non-representative
sample of subjects or selection of tasks,
inconsistent testing procedures) - Apply statistical methods to data analysis
- Resolve the practical problem, refine the theory,
and give advice to future researchers
94Controlled Psychologically-oriented Experiments
- Managers of actively used systems are coming to
recognize the power of controlled experiments in
fine tuning the human-computer interface. - Limited time, and then performance could be
compared with the control group. Dependent
measures could include performance times,
user-subjective satisfaction, error rates, and
user retention over time.
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