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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 6750

Cognitive 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