User Modeling

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User Modeling

• CIS 376
• Bruce R. Maxim
• UM-Dearborn

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What is HCI?

• Answer human computer interaction
• Not just human factors
• No strong agreement
• Main emphasis of HCI is user interface design

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User interface involves

• Hardware
• Behavior of software
• Supporting documentation

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Typical Human Factors Measures

• Time to learn
• Speed of performance
• User error rates
• Retention over time
• Subjective satisfaction

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Where do user interfaces come from?

• Designed by programmers
• Functionality dominates software design and
  marketing
• Designer intuition is often used rather than user
  modeling (not good)

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HCI Goals for Designers

• Improve user's quality of life by building
  quality (not flashy) interactive systems
• Promote attention to user interface issues which
  should be considered by managers
• Become successful designers of systems that go
  beyond intuitive concepts like "user
  friendliness" and focus on supporting the user's
  real task goals

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Motivation for Including Human Factors in User
Interface Design

• Life critical systems
• Industrial and commercial uses
• Personal applications
• Exploratory, creative, and cooperative systems

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Accommodating Human Diversity in Design

• Physical workspaces
• Cognitive and perceptual ability differences
• Personality differences
• Cultural and international diversity
• User disabilities
• Elderly users

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US Military Standards for Human Engineering and
Design

• Achieve required performance
• Minimize personnel training requirements
• Achieve required reliability
• Foster design standardization

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How is this done?

• Ensure functionality by basing design on user
  task analysis
• System reliability requires designer attention to
  details like privacy, security, and data
  integrity
• Standardization requires attention to issues like
  system integration, consistency, and portability
• Schedule and budget must allow for human factors
  work like user analysis and testing

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Approaches to User Interface Design

• Human Factors prototype and test
• Cognitive theory production system
• Engineering models
• KLM (keystroke level model)
• GOMS Models (goals, operators, methods, selection
  rules)

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Keystroke Level Model (KLM)

• Choose representative user task scenarios
• Specify design to point that keystrokes defining
  actions can be listed
• List keystrokes (operators) required to perform
  task
• Insert mental operators at points user needs to
  stop and think
• Look up standard execution time for each operator
• Add up the execution times for the operators
• Total is estimated time to complete task

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Standard Execution Times

• K - key press (0.2 sec 55 wpm)
• P - point with mouse (1.1 sec)
• B - mouse button press (0.1 sec)
• BB - press and release button (0.2 sec)
• H - home hands to keyboard or mouse (0.4 sec)
• M - mental act of thinking (1.2 sec)

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Current Design Delete a file by dragging it to
the trash icon

• 1. Point to file icon (P)
• 2. Press hold mouse button (B)
• 3. Drag file to trash icon (P)
• 4. Release mouse button (B)
• 5. Point to original window (P)
• 3P 2B 3.5 sec.

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New Design Adding a command to menu

• 1. Point to file icon (P)
• 2. Click button (BB)
• 3. Point to file menu (P)
• 4. Press and hold button (B)
• 5. Point to delete command (P)
• 6. Release mouse button (B)
• 7. Point to original window (P)
• 4P 4B 4.8 sec.

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Assumptions

• These previous scenarios work only work if the
  user is currently able to view all the needed
  windows and icons.
• If the trash icon for example is buried under
  other windows the first procedure is slowed down
  quite a bit.

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Inserting Mental Operators Where does the user
stop and think?

• 1. Initiating a process.
• 2. Making strategic decisions.
• 3. Retrieving a chunk from users short term
  memory
• 4. Finding something on the screen.
• 5. Verifying intended action is complete.

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Mental Operators New vs Experienced Users

• New users stop and check feedback after every
  step
• New users have small chunks
• Experienced users have elaborate chunks
• Experienced users may overlap mental operators
  with physical operators

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Delete a file by dragging icon to trash

• 1. Initiate delete. (M)
• 2. Find file icon. (M)
• 3. Point to file icon. (P)
• 4. Press hold button. (B)
• 5. Verify icon reverse video. (M)
• 6. Find trash icon. (M)
• 7. Drag file to trash icon. (P)

• 8. Verify trash reverse video. (M)
• 9. Release button. (B)
• 10. Verify bulging trash icon. (M)
• 11. Find original window. (M)
• 12. Point to window. (P)

3P 2B 7M 12.6 sec.
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Placement of Mental Operators

• Hard to do - requires good intuition from
  designer
• Consistency in the number of Mental's assigned is
  more important than exact positioning

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GOMS ModelGoals Operators Methods Selection Rules

• Advanatges
• GOMS models are executable
• GOMS models allow simulated execution of user
  task
• Provide a rigorous description of what user must
  learn
• Provide estimate of size or complexity of
  interface (number of distinct methods and their
  length)
• Can estimate both learning time (about 30 sec per
  step and execution time (total of KLM operators)
• Allow designer to evaluate the effect of reusing
  or sharing methods among several tasks

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• This example is extracted from
• David Kieras, A Guide to GOMS Task Analysis,
• University of Michigan Technical Report,
• Spring, 1994.

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User Goals

• Delete a file.
• Move a file.
• Delete a directory.
• Move a directory.

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• To accomplish goal of deleting a file
• 1. Accomplish goal of dragging file to trash.
• 2. Return with goal completed.
• To accomplish goal of moving a file
• 1. Accomplish goal of dragging file to
  destination.
• 2. Return with goal completed.

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• To accomplish goal of deleting a directory
• 1. Accomplish goal of dragging directory to
  trash.
• 2. Return with goal completed.
• To accomplish goal of moving a directory
• 1. Accomplish goal of dragging directory to
  trash.
• 2. Return with goal completed.

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Generalized Methods

• Method for accomplishing goal of deleting an
  object
• 1. Accomplish goal of dragging object to trash.
• 2. Return with goal completed.
• Method for accomplishing goal of moving an
  object
• 1. Accomplish goal of dragging object to
  destination.
• 2. Return with goal completed.

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Sub Method

• Accomplish goal of dragging item to destination
• 1. Locate icon on screen.
• 2. Move cursor to item icon location.
• 3. Hold mouse button.
• 4. Locate destination icon.
• 5. Move cursor to destination icon.
• 6. Verify destination icon reverse video.
• 7. Release mouse button.
• 8. Return with goal accomplished.

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Method for GOMS Model Construction

• Make a list of top-level user goals
• Write a step-by-step method for accomplishing
  each goal on list
• Continue refining each step that is not a
  keystroke level operator by defining it as a
  subgoal and add it to the list of user goals
• Continue processing user goals until list is
  empty (meaning that all user goals are defined in
  terms of keystrokes)
• If there are multiple methods to accomplish a
  goal supply decision rules to choose which method
  to invoke