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Errors & Help. Dr. A. Rauf. Slips versus Mistakes. Recall: Human errors can be classified into slips and mistakes Can understand using Norman’s gulf of execution

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errors help


Dr. A. Rauf

slips versus mistakes
Slips versus Mistakes
  • Recall:
    • Human errors can be classified into slips and mistakes
  • Can understand using Norman’s gulf of execution
    • SLIP: If you understand a system well you may know exactly what to do to satisfy your goals: you’ve formulated the correct action. But you may fail to execute that action correctly (mis-type, press the wrong button)
    • MISTAKE: If you don’t know the system well you may not even formulate the right goal. (Example: you may pick the magnifying glass icon thinking it is the ‘find’ function, when it actually zooms the text).
  • Both may be corrected for, and designed around.
errors in user computer dialog
Errors in User-Computer Dialog
  • Three phases
    • Read-scan phase -- Perceptual errors
    • Think phase -- Cognitive errors
    • Respond phase -- Motor errors
  • Can generally lead to either slips or mistakes
perceptual errors
Perceptual Errors
  • Result from poor perceptual cues
    • Display of objects that are visually similar
    • Invisible or poorly expressed states
    • Failure to capture user’s attention
    • Lack of perceivable feedback
cognitive errors
Cognitive Errors
  • Caused by taxing memory and thinking
    • Tax recall memory
    • Poor mnemonic aids
    • Inconsistency
    • Lack of context or status info
      • e.g., where came from in a menu
    • Mental calculations and translations
cognitive errors1
PSYCH / CS 6750Cognitive Errors

Are cognitive errors likely here?

motor errors
Motor Errors
  • Taxing the motor skills
    • Awkward movements
    • Highly similar motor sequences
      • e.g., double click, click
    • Pressure for speed
    • Require a high degree of hand-eye coordination
    • Requiring special types of motor skills (type)
motor errors1
Motor Errors

Lots of errors are likely here!!

example studies
Example Studies
  • 170 experienced UNIX users over 9 days
    • Individual commands error rates of 3-50%
  • 300 security system users over 20 months
    • 12,117 error messages
    • Most common 11 errors -> 65%
    • 2517 involved repeated errors (with no non-errors in between) within 10 minutes
      •  Bad error recovery/help

Kraut et al, CHI ‘83

Mosteller & Ballas, Human Factors ‘89

  • Automatic (subconscious) error that occurs without deliberation
  • Examples?
types of slips
Types of Slips
  • 1. Capture error
    • Continue frequently done activity instead of intended one
      • Type “animation” instead of animate
      • Confirm deletion of file instead of cancel
  • 2. Description error
    • Intended action has much in common with others possible (usually when distracted, close proximity)
      • ctrl key & caps lock key / Sun & Mac
types of slips1
Types of Slips
  • 3. Data driven error
    • Triggered by arrival of sensory info which intrudes into normal action
      • Call to give someone a number, dial that number instead
  • 4. Associative activation
    • Internal thoughts and associations trigger action
      • Phone rings, yell “come in”
types of slips2
Types of Slips
  • 5. Loss of activation
    • Forgetting goal in middle of sequence of actions
      • Start going into room, then forget why you’re going there
  • 6. Mode errors
    • Do action in one mode thinking you’re in another
      • Delete file, but you’re in wrong directory
error handling strategies
Error-handling Strategies
  • Avoid and prevent
  • Identify and understand
  • Handle and recover
preventing errors
Preventing Errors
  • Rules of thumb:
    • Preventing slips can be done by analysing users’ interaction with the application, then tweaking screen design, button spacing, etc.
    • Preventing many mistakes requires that users understand the system better; may require more radical redesign, or perhaps a totally different metaphor
error prevention guidelines
Error Prevention Guidelines
  • Eliminate modes or provide visible cues for modes
  • Use good coding techniques (color, style)
  • Maximize recognition, minimize recall
  • Design non-similar motor sequences or commands
  • Minimize need for typing
error prevention guidelines1
Error Prevention Guidelines
  • Test and monitor for errors and engineer them out
  • Allow reconsideration of action by user (e.g., removing file from trash)
error prevention guidelines2
Error Prevention Guidelines
  • Provide appropriate type of feedback
    • Gag - Prevent user from continuing
      • Erroneous login
error prevention
Error prevention

Warn user an unusual situation is occurring

  • Bell or alert box
error prevention1
Error prevention
  • Nothing - Just don’t do anything (Careful, user must determine problem)
    • Mac: move file to bad place
error recovery guidelines
Error Recovery Guidelines
  • Provide undo function
  • Provide cancel function from operations in progress
  • Require confirmation for drastic, destructive commands
  • Provide reasonableness checks on input data
    • Did you really mean to order 5000?
error recovery guidelines1
Error Recovery Guidelines
  • However, before a user can recover, must be able to detect that an error has occurred
    • Detection: provided by easy visibility, feedback
  • Other options?
    • Self-correct - Guess correct action & do it
      • Spell-check correction
    • Dialog - System opens dialog with user
      • Go into debugger on run-time crash
  • Query - Ask user what should’ve been done, then allow error action as legal one (“did you mean…?”)
      • Command language naming error
error recovery guidelines2
Error Recovery Guidelines
  • Return cursor to error field, allow fix
    • Tell them what to fix, how to fix it
  • Provide some intelligence
    • Guess what they wanted to do
  • Provide quick access to context-sensitive help
error handling example web
Error Handling Example (Web)
  • Form fill in is the most common error case
command prompts
Command Prompts
  • In CL interfaces, usage prompts are an example.
  • Assumes that
    • system can detect error
    • user understands the command well enough to apply the guidance
  • Generally only helpful for simple errors