A critical task is, according to the FDA human factors guidance, a user task whose erroneous or omitted performance would or could lead to serious harm to the patient or user. Harm here also includes compromised medical care. The classification remains in place even if alarms, plausibility checks or other risk control measures are present. These reduce the risk but do not remove the criticality of the task itself. Critical tasks determine which use scenarios must be tested in the summative evaluation.
What makes a task critical
It is not the frequency of a possible error that decides the classification as a critical task but the severity of its possible consequences. A task in which an error occurs rarely but could lead to serious or irreversible harm if it does is critical, even if it hardly stands out in everyday testing. Conversely, a task that is frequently error-prone but without consequences is not critical in the sense of this definition, even if it should be improved for reasons of comfort.
“Harm” is deliberately defined broadly here and, besides direct harm to the patient, also includes compromised medical care, for example a delayed or interrupted treatment that in itself does not yet constitute a direct injury but endangers the security of care.
How critical tasks are identified
Critical tasks are not determined in isolation but are the result of the upstream chain of analysis: The task analysis provides the complete list of candidates, and the use-related risk analysis assesses for each task the possible use errors and their consequences.
A combination of two perspectives has proved effective in practice: the systematic review of all tasks with the question “What if an error occurs here and no countermeasure takes effect?”, and the comparison with known problems of comparable products from post-market surveillance and incident databases. A purely internal assessment without this external comparison tends, in experience, to overlook error patterns that are already known in the field.
Critical task and hazard-related use scenario
Between the FDA terminology and the terminology of IEC 62366-1 there is a close but not always congruent correspondence. What the FDA calls a critical task is closely related to the hazard-related use scenario from IEC 62366-1: a scenario in which a use error can lead to a hazardous situation. The two terms are, however, not synonymous: A critical task can be part of a hazard-related use scenario but describes the task itself, whereas the scenario depicts the complete chain of error, hazardous situation and possible harm. Critical tasks are also often directly linked to risk control measures and are therefore examined specifically in formative and summative evaluations. The MDR does not use the term critical task explicitly; the identification of safety-relevant user interactions does, however, support the requirements for risk management and ergonomic design according to Annex I.
The difference lies in the perspective: The critical task is task-centered and names the action in which care is decisive. The hazard-related use scenario is event-centered and describes the complete sequence of error, hazardous situation and possible harm. For manufacturers documenting according to both IEC 62366-1 and FDA requirements, it is common to consolidate both terminologies in a joint table to avoid duplicate work.
Prioritization instead of a claim to completeness
A widespread misunderstanding is to classify as many tasks as possible as critical in order to be on the safe side. The opposite is the case: The classification as critical has direct consequences for the scope and cost of the summative evaluation, and an excessively broad list dilutes attention precisely for the tasks that actually carry the greatest risk.
A robust classification requires a comprehensible justification per task of why exactly this error could lead to exactly this harm, instead of a blanket safety margin. This discipline pays off in the review by a notified body (the EU conformity assessment body) or the FDA: A justified, focused list of critical tasks is more convincing than a long list without a recognizable selection logic.
Consequences for the summative evaluation
The list of critical tasks directly determines the testing scope of the summative usability evaluation: Each critical task must be tested there with a sufficient number of representative users under realistic conditions. If a previously unidentified use error occurs, both a design change and a renewed test are, as a rule, required.
This is why care in identifying critical tasks pays off particularly early in the process: An overlooked critical task is not tested, and the risk remains undetected until, in the worst case, it becomes visible only in the field, through post-market surveillance and incident reports.
Regulatory reference
The FDA human factors guidance requires an explicit, documented list of critical tasks as the basis for the test plan of the human factors validation and puts these tasks at the center of the authority's assessment of marketing submissions.
According to IEC 62366-1, the requirement in terms of content corresponds to the identification of hazard-related use scenarios within the use-related risk analysis, without using the term “critical task” itself. Through the use-related risk analysis, the classification is also interlinked with risk management according to ISO 14971.
A critical task is not a particularly error-prone task but one whose failure could have serious harm as a consequence. Its identification is the result of task analysis and use-related risk analysis, not a separate exercise.
It directly determines what must be tested in the summative evaluation. An overlooked critical task remains untested until, in the worst case, the risk becomes visible only in the field.
Frequently asked questions (FAQ)
Is every task with a risk automatically a critical task?
No. Many tasks involve risks. Those classified as critical tasks are typically the ones in which a use error can lead to a hazardous situation or harm.
What distinguishes a critical task from a hazard-related use scenario?
Both describe similar matters in content from different perspectives: The critical task (FDA terminology) is task-centered and names the action. The hazard-related use scenario (IEC 62366-1) is event-centered and describes the complete error-hazard-harm sequence. Manufacturers for both markets usually consolidate them in a joint table.
Should you classify as many tasks as possible as critical to be safe?
No. An excessively broad list dilutes attention precisely for the tasks that carry the most risk and drives up the validation effort unnecessarily. A focused list, justified comprehensibly for each task, is both more robust in content and more convincing toward reviewing bodies.
What happens if a critical task fails in the summative evaluation?
If a safety-relevant use error occurs with a critical task, both a design change and a renewed validation are generally required, with corresponding consequences for schedule and budget. This is the main reason to address critical tasks specifically already in early formative evaluations.
Is the development team's internal assessment sufficient to identify critical tasks?
Not on its own. The combination of a systematic internal review of all tasks and a comparison with known problems of comparable products from post-market surveillance and incident databases has proved effective. A purely internal view tends, in experience, to overlook error patterns that are already documented in the field.
Do you want to make sure your validation study tests exactly the tasks that really count? We identify critical tasks systematically and with justification.
More about our usability engineeringSources
- IEC 62366-1:2015+AMD1:2020, Medical devices, Part 1: Application of usability engineering to medical devices
- ISO 14971:2019, Medical devices, Application of risk management to medical devices
- Regulation (EU) 2017/745 on medical devices (MDR)
- FDA Guidance: Applying Human Factors and Usability Engineering to Medical Devices