Human factors engineering, also called usability engineering, is the discipline of designing devices around the capabilities and limitations of the people who will actually use them. In medical devices it is a regulatory requirement, structured by IEC 62366-1, because use error is one of the most common causes of device-related harm.
The key distinction the field makes is between user error and use error. User error implies the person was at fault. Use error is a system property: if a device allows a tired clinician at three in the morning to select the wrong dose unit, the design has failed, not the individual. Regulators expect manufacturers to engineer out the possibility rather than train around it.
Formative work is exploratory and can use small numbers of participants, prototypes and think-aloud protocols. Summative validation is confirmatory: it uses production-equivalent devices, representative users from each distinct user group, realistic simulated environments and a defined number of participants per group. Failures observed during summative testing must be analysed for root cause, and design fixes generally require re-validation.
Forcing functions that make an unsafe action impossible, defaults that fail safe, clear differentiation of similar-looking items, confirmation steps reserved for genuinely irreversible actions, alarms that are informative rather than merely loud, and instructions written for the actual reading level and conditions of use. Alarm fatigue in particular is a well documented hazard: a device that alerts too often trains its users to ignore it.
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