User Interface Design

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User Interface Design

• Southern Methodist University
• CSE 8316
• Spring 2003

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Temporal Relations and Usability Specifications
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Introduction

• 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.

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Introduction

• UAN can be used to specify
• Sequence
• Iteration
• Optionality
• Repeating choice
• Order independence
• Interruptibility
• Interleavability
• Concurrency
• Waiting

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Sequencing 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

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Abstraction

• 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

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Abstraction

• 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.

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Task Operators

• Choice
• Simple choice is represented in UAN with the
  vertical bar, '.
• Repeating choice is formed by adding the
  iterators ' and '.

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Task 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 '.

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Task 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.

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Task 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'.

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Task 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.

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Task Operators

• Concurrency
• If two tasks can be performed in parallel (e.g.
  two different users), then tasks are concurrent
  Represented with '.

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Task 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'

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Other 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

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Design 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

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Usability Specifications
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Usability 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

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Usability 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

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Usability 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

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Usability 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

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Usability 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

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Measuring 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

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Benchmark 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

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Questionnaire

• Quantitative measure for subjective feelings
• Creating survey that provides useful data is not
  trivial
• Recommend use of scientifically created question
  (e.g. QUIS)

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Values 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

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Values 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

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Setting 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

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Current 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

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Worst 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

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Worst 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

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Planned 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

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Best 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

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Observed Results

• Actual values obtained from user testing
• Provides quick comparison with projected levels

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Setting 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

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Setting Levels

• The context of the task is important in
  determining these levels

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Example 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
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Example 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
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Example 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
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Cautions

• 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

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Cautions

• 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

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Expert Reviews, Usability Testing, Surveys, and
Continuing Assessment
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Introduction

• 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

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Introduction

• 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)

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Introduction

• costs of product and finances allocated for
  testing
• time available
• experience of the design and evaluation team

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Introduction

• 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.

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Expert 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.

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Expert Reviews

• There are a variety of expert review methods to
  chose from
• Heuristic evaluation
• Guidelines review
• Consistency inspection
• Cognitive walkthrough
• Formal usability inspection

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Expert 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.

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Expert Reviews

• The dangers with expert reviews are that the
  experts may not have an adequate understanding of
  the task domain or user communities.

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Expert 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.

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Usability 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.

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Usability Testing and Laboratories

• The movement towards usability testing stimulated
  the construction of usability laboratories.

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Usability 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).

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Usability Lab (Interface Analysis Associates)
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Usability Lab (Interface Analysis Associates)
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Usability 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.

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Usability 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.

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Usability 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.

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Usability 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

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Nomos Lab
An observer's view of a test being carried out in
the purposely designed Nomos lab.
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Nomos Lab
Two sides of the one-way glass - actions and
problems are logged while the user carrys out
real tasks with the product.
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Usability 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

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Usability 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

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Usability 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.

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Siemens 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.
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Siemens 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.
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Inventory 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.

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Inventory 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.

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Surveys

• 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.

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Surveys

• 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.

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Surveys

• 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)

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Surveys

• 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).

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Surveys

• 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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Summary

• 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

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Product Evaluations
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Evaluation 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.

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Evaluation During Active Use
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Evaluation 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.

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Evaluation 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.

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Evaluation 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.

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Evaluation 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.

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Evaluation 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.

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Evaluation 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.

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Evaluation 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.

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Evaluation 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.

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Controlled 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.

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Controlled 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

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Controlled 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

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Controlled 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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