Use environment factors (German: Störfaktoren) are environmental and contextual factors of the use environment that can influence the interaction with a medical device, such as noise, lighting, time pressure, interruptions or wearing gloves. If tests ignore them, they systematically overestimate the actual usability.
Not every characteristic of the use environment is automatically a use environment factor; it becomes relevant only when it can impair perception, decision-making or the execution of actions.
Why ignored use environment factors distort tests
A usability test in a quiet, well-lit test room does not measure the same task as actual use in the hectic everyday routine of a clinic, even if the operating steps and test participants are identical. Cognitive load, the perceptibility of signals and motor precision change considerably under real conditions, and it is precisely this change that explains many use errors that occur in the field but were never observed in the test room.
The problem is tricky because a test conducted under ideal conditions can be formally successful (all participants solve the task without errors) and still create a false sense of safety. The actual usability of the product is thereby neither disproved nor proven: It simply remains untested for exactly the conditions under which the product is actually used.
Categories of use environment factors
- Physical environment: lighting, noise level, temperature, cramped spaces, vibration.
- Temporal conditions: time pressure, night shifts, fatigue after long working hours.
- Interruptions: phone calls, parallel alarms from other devices, questions from colleagues, a change of responsibility in the middle of the task.
- Physical limitations of the user: gloves, protective clothing, restricted vision caused by a mask or visor.
- Social and organizational factors: the presence of several people, hierarchical barriers to communication, parallel responsibilities.
- Concurrent tasks: operating the product while simultaneously monitoring the patient or other devices.
These categories are not mutually exclusive: An emergency scenario typically combines time pressure, interruptions and high social complexity at the same time, with an effect that goes well beyond the sum of the individual factors.
How relevant use environment factors are identified
The selection of use environment factors relevant to a product does not come from a generic checklist but from the context analysis and the workflow analysis: On-site observation shows which conditions actually occur at a specific place of use, instead of assuming them. A product for the intensive care unit and an identical product for home use are in fact exposed to different use environment factors, even if the operating logic is the same.
Borderline and exceptional situations are particularly revealing: Emergency use, night shifts and situations with reduced staffing typically bundle several use environment factors at once and are therefore especially informative about where a design actually holds up under real conditions.
Reproducing use environment factors in the test design
Not every use environment factor can be recreated one to one in the lab, but many can be approximated with reasonable effort: reduced lighting, played-back ambient noise, a side task to be handled in parallel to create time pressure, wearing gloves, or a planned interruption in the middle of the task.
What matters is that these conditions are not added cumulatively “to be on the safe side” but specifically reproduce those that were identified as real and relevant in the context analysis. A test that piles up arbitrary aggravating conditions without justifying them from the real context of use produces results that are just as unreliable as a test under ideal conditions. It overestimates the problem instead of the usability.
Not every use environment factor belongs in every test
Formative and summative studies have different requirements for reproducing use environment factors. In early formative evaluations, the focus is on understanding design problems, which is why reduced conditions are often sufficient to uncover fundamental weaknesses. In the summative evaluation, by contrast, those use environment factors should be considered that are relevant to the selected hazard-related use scenarios and to the assessment of use-related risks. What decides is not the number of reproduced factors but their relevance to real use.
A sensible prioritization also takes into account the interaction between use environment factor and task: A factor that makes an uncritical routine task slightly harder deserves less reproduction effort than one that opens up additional sources of error for a critical task.
Regulatory reference
IEC 62366-2 explains, as a guidance document and using examples, how relevant use environment factors of the real context of use can be included in formative and summative test designs; as a technical report, however, it contains no standalone normative requirements. The use environment is also part of the use specification according to IEC 62366-1 and must accordingly be taken into account in the use-related risk analysis.
The FDA Human Factors Guidance expects the use environment to be adequately represented in human factors validation testing, including aggravating factors that are typical of the intended use. Test conditions should be realistic enough to reflect the actual conditions of use.
Use environment factors are the conditions under which a product is actually used, not those under which it is easiest to test. A test that ignores them systematically overestimates usability and risks real use errors becoming visible only in the field.
Which use environment factors are relevant follows from context and workflow analysis on site, not from a generic list and not from arbitrarily piled-up aggravating conditions.
Frequently asked questions (FAQ)
Why is a test under ideal conditions not enough?
Because cognitive load, perceptibility and motor precision can differ considerably under real conditions. A test in a quiet test room can be formally successful and still create a false sense of safety, because usability under the conditions of actual use simply remains untested.
How are the relevant use environment factors for a product determined?
Through context analysis and workflow analysis on site, not through a generic checklist. Observation at the real place of use shows which conditions actually occur: A product for the intensive care unit is exposed to different use environment factors than an identical product for home use.
Do all use environment factors have to be reproduced in every test?
No. In formative evaluations, reduced conditions are often enough to uncover fundamental design problems. In the summative evaluation, those use environment factors should be considered that are relevant to the selected hazard-related use scenarios and to the assessment of use-related risks. What matters is their relevance to real use, not the number of reproduced factors.
Can you build too many aggravating conditions into a test?
Yes. Arbitrarily piled-up use environment factors with no connection to the real context of use produce results that are just as unreliable as a test under ideal conditions. They overestimate the problem instead of measuring actual usability. What counts is the justification from the context analysis, not a blanket aggravation.
Do you want to know how your product can actually be operated under real conditions of use? We make relevant use environment factors visible through context analysis and realistic tests.
More about our UX researchSources
- IEC 62366-1:2015+AMD1:2020, Medical devices, Part 1: Application of usability engineering to medical devices
- IEC/TR 62366-2:2016, Medical devices, Part 2: Guidance on the application of usability engineering to medical devices
- FDA Guidance: Applying Human Factors and Usability Engineering to Medical Devices