Error Models & User Errors
Errors are part of interacting with digital systems - but they are not a sign of stupidity, they can be systematically explained. UX design must understand and intercept them.
Definition
A user error is an unintentional action or an incorrect result that occurs when using a system - regardless of whether the system works “correctly”.
Norman: Slips vs. Mistakes
Donald A. Norman distinguishes between two basic types of errors:
🟢 Briefs - “slips”
Error when executing an intention that is actually correct Example: wrong button clicked, although the destination was clear
🔴 Mistakes - “wrong decisions”
Error due to incorrect intention or assumption Example: User:in thinks “Back” means “Cancel” - but it doesn’t
Implications for Design
Slips are often caused by poor affordances or unclear feedback. Mistakes due to incorrect mental models or misleading navigation.
Reason: Human Error as a System Component
James Reason makes a distinction in his error model:
-
Wissensbasierte Fehler (Knowledge-based mistakes) in unknown situations → incorrect interpretation
-
Regelbasierte Fehler (Rule-based mistakes) known rule applied incorrectly
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Skill-based slips (Skill-based slips) Familiar action automated, but incorrect (e.g. mistyping)
Design Against Errors
| Principle | Implementation |
|---|---|
| Error tolerance | Undo, restore, queries before deletion actions |
| Feedback & status displays | What has been done? What is happening right now? |
| Error avoidance instead of error handling | Deactivate buttons instead of showing warning later |
| Consistency | Recognizable symbols, navigation, layouts |
| Explicit labeling | ”Cancel” instead of “Back” |
Practical Example
An e-mail system allows deletion without consultation.
→ User accidentally deletes important message.
Better: “Recycle bin” with undo function and query for sensitive content.
Conclusion
User errors do not occur because people are unfocused or incompetent - but because systems are designed to be complex, ambiguous or error-prone.
UX design should focus on being error-friendly rather than error-free.
Take Home Message
Errors are systemic - not individual. Good design makes mistakes unlikely and reversible.
Last modified: 17 June 2025