The Interface Paradox

Key Insights

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• The Interface Error Amplification Factor (IEAF) is defined as: Maximum consequence severity of an interface error ÷ Minimum action complexity required to reach that error state (measured in control inputs, keystrokes, or clicks).
• The IEAF of a single-cursor EHR dose-entry field with a 10× unit dropdown is higher than the IEAF of the locked glass medication cabinet it replaced, because the physical key created mandatory action complexity the GUI removed.
• Boeing 737 MAX MCAS had an effective IEAF approaching infinity for any single angle-of-attack sensor failure: one faulty sensor input, zero required pilot actions, and maximum consequence.
• Protective friction — deliberately inserted action complexity between a user and a dangerous outcome — is the design principle that produces low-IEAF systems; it is absent from most commercial digital interface design doctrines.
• The most dangerous interface designs are not those that require the most steps — they are those that route the fewest steps to the most severe outcomes.

References

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