Errors & Help

1. Errors&Help Dr. A. Rauf

2. 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.

4. 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

5. 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

6. 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

7. PSYCH / CS 6750 Cognitive Errors Are cognitive errors likely here?

8. 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)

9. Motor Errors Lots of errors are likely here!!

10. 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

11. Slips • Automatic (subconscious) error that occurs without deliberation • Examples?

12. 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

13. 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”

14. 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

15. Error-handling Strategies • Avoid and prevent • Identify and understand • Handle and recover

16. 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

17. 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

18. Error Prevention Guidelines • Test and monitor for errors and engineer them out • Allow reconsideration of action by user (e.g., removing file from trash)

19. Error Prevention Guidelines • Provide appropriate type of feedback • Gag - Prevent user from continuing • Erroneous login

20. Error prevention Warn user an unusual situation is occurring • Bell or alert box

21. Error prevention • Nothing - Just don’t do anything (Careful, user must determine problem) • Mac: move file to bad place

22. 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?

23. 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

24. 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

25. Error Handling Example (Web) • Form fill in is the most common error case

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27. 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