Design inputs are the documented requirements for a medical device that serve as the basis for its development. They result, among other things, from the intended purpose (intended use), user needs, regulatory requirements, technical constraints, and findings from risk management and usability engineering. Design outputs are the documented development results that emerge from these requirements. Examples include drawings, specifications, software artifacts, labeling, or instructions for use.
Design inputs thus describe what the product must fulfill. Design outputs document how these requirements were implemented in the product or in its specifications. A traceable link must exist between the two so that the implementation of the requirements can be verified.
Design inputs in the usability engineering process
In usability engineering, design inputs do not arise in isolation. They are derived, among other sources, from the use specification, the analysis of the context of use, user needs, known use errors, findings from post-market surveillance, and the use-related risk analysis.
The quality of these requirements directly influences the later safety and usability of the product. Incomplete, contradictory, or overly general design inputs can lead to relevant requirements for the user interface not being implemented adequately, or to safety-critical use scenarios being recognized only late.
Usability-relevant design inputs typically come from:
- User research
- Context analyses
- Field observations and interviews
- Task and workflow analyses
- Complaint and vigilance data
- Analyses of comparable products
- Use-related risk analyses
- Formative evaluations
The results of formative evaluations can also lead to new or revised design inputs. Design inputs should therefore be reviewed regularly over the course of development and updated in a controlled manner when new findings emerge.
Design inputs versus user needs
A common mistake is to equate user needs and design inputs.
User needs describe what users require or must achieve in the respective context of use. They are first formulated from the users' perspective and may deliberately be kept general.
Design inputs then translate these needs into concrete, verifiable requirements for the product. Example: From the user need "The user must be able to set the intended medication dose reliably, even under time pressure," the following design inputs can be derived, for instance:
- The dose that has been set must be displayed unambiguously before delivery.
- Confirmation of the dose must be separate from triggering the medication delivery.
- Dose values and dose units must be displayed together.
- A defined plausibility check must be performed for safety-relevant entries.
Design inputs must be sufficiently unambiguous and precise so that design outputs and suitable verification criteria can be derived from them.
Many usability-relevant design inputs also arise directly from risk management. If use-related hazards or hazard-related use scenarios are identified, they can give rise to requirements for the user interface, operating logic, alarms, labeling, training, or other risk control measures.
Design output as the implementation of requirements
In the design and development process, design outputs are the documented implementation of the design inputs.
While design inputs define which requirements the product must fulfill, design outputs describe the resulting product or its components precisely enough that they can be manufactured, implemented, inspected, installed, or maintained.
Design outputs thus form an essential basis for:
- Design verification
- Design validation
- Design transfer
- Manufacturing and quality control
- Installation and service
- Change management
- Regulatory traceability
Usability-relevant requirements must be reflected in concrete design outputs. From a design input such as "Confusion between different doses must be prevented or reduced as far as possible," the following design outputs can arise, for example:
- Specification of the dose display
- Interaction logic for selection and confirmation
- Rules for permissible dose ranges
- Warning and error messages
- Interlock or confirmation mechanisms
- Design of the labeling
- Corresponding software and user interface specifications
A single design input can lead to several design outputs. Conversely, one design output can implement several requirements at the same time.
Typical design outputs for medical devices
Depending on the type of product and the development process, design outputs can comprise different artifacts:
- Hardware drawings and design documentation
- Material and component specifications
- Software architecture and software specifications
- User interface specifications
- Display and screen specifications
- Operating and interaction sequences
- Alarm and error message specifications
- Labeling and packaging
- Instructions for use and accompanying documentation
- Test methods and test specifications
- Production and assembly instructions
- Installation, maintenance, and service instructions
From a human factors perspective, the specified, use-relevant characteristics of the user interface are among the important design outputs. Examples include:
- Operating logic
- Information presentation
- Input and confirmation mechanisms
- Alarm limits and alarm design
- Dosing algorithms
- Interlock mechanisms
- Warnings
- Labeling
- Physical controls
- Safety-relevant software functions
These design outputs are often directly linked to hazards, hazardous situations, and risk control measures from the risk management file.
The importance of acceptance criteria
Design inputs must be formulated so that it can be checked whether the resulting design outputs meet the requirements.
Statements such as "The display must be easy to read," "The product must be intuitive to operate," or "The user guidance must be simple" are generally not sufficient for this. They leave open under which conditions and on the basis of which criteria fulfillment of the requirement is to be assessed.
Suitable requirements and acceptance criteria can relate, for example, to:
- Character size
- Contrast
- Viewing distance
- Lighting conditions
- Response time
- Number of required action steps
- Permissible input ranges
- Perceptibility of alarms
- Unambiguous system feedback
- Error tolerance of the operating logic
Criteria should not be chosen merely because they are technically easy to measure. They must be technically justified and fit the intended user, the context of use, and the use-related risk.
Not every user-related requirement can be assessed completely with a single technical metric. While clearly specified technical requirements are checked by design verification, design validation assesses whether the resulting product meets the user needs and the requirements of the intended application under representative conditions.
Typical weaknesses in practice
In development projects, design inputs are often formulated too generally, too technically, or without sufficient reference to the user, the context of use, and the use-related risk. Typical weaknesses are:
- Missing traceability between user needs, design inputs, and design outputs
- Missing link between risk control measures and development requirements
- Mixing of design inputs and design outputs
- Solution-oriented formulation of design inputs without a traceable originating requirement
- Incomplete user interface specifications
- Ambiguous or non-verifiable design inputs
- Missing or unsuitable acceptance criteria
- Undocumented design changes
- Inadequate identification of safety-relevant requirements and outputs
- Insufficient coordination between human factors, development, quality management, and risk management
- Traceability not updated after design changes
Especially for software and interactive medical devices, it is often found that user interfaces have been implemented but not specified sufficiently. Screenshots or implemented software versions alone do not replace a controlled user interface specification. It should describe the relevant states, content, interactions, system responses, error messages, and dependencies so that the implementation can be traced and verified.
Regulatory reference
ISO 13485:2016 addresses design inputs and design outputs within its requirements for design and development. Among other things, design inputs must take into account functional, performance, safety, regulatory, and other requirements essential for the product. They must be reviewed, approved, and formulated so that they are unambiguous, complete, and not in conflict with one another.
Design outputs must meet the design inputs, provide information for purchasing, production, and service, contain or reference acceptance criteria, and specify the product characteristics that are essential for safe and proper use (in the EU: use in accordance with the intended purpose).
IEC 62366-1 places the development and evaluation of the user interface within a risk-based usability engineering process. The use specification, safety-related user interface characteristics, known or foreseeable use errors, hazard-related use scenarios, and the user interface specification provide important foundations for usability-relevant design inputs and outputs.
ISO 14971 requires that risk control measures be implemented and that their implementation and effectiveness be verified. Risk control measures can therefore lead to design inputs and must be traceably reflected in corresponding design outputs and verification evidence.
For the US market, the FDA Quality Management System Regulation (QMSR) has applied since February 2, 2026. It incorporates the requirements of ISO 13485:2016 into 21 CFR Part 820. Requirements for design and development now result in particular from 21 CFR 820.10 and ISO 13485:2016, Section 7.3. The former reference to 21 CFR 820.30 for design controls is therefore no longer current; the corresponding sections are reserved in the current structure.
Design inputs define what a medical device must fulfill. Design outputs document how these requirements were implemented in the product or in its specifications.
Continuous traceability connects: user needs → design inputs → design outputs → verification and validation.
Only when requirements are formulated unambiguously, implemented traceably, and verified appropriately can it be shown in a regulatorily robust way that the medical device meets the intended requirements and can be used safely.
Frequently asked questions (FAQ)
Are user needs and design inputs the same thing?
No. User needs describe the needs, goals, or expectations of users. Design inputs translate these, together with further regulatory, technical, and safety-related requirements, into concrete, verifiable development requirements.
What is the difference between design input and design output?
Design inputs describe which requirements a product must fulfill. Design outputs are the documented development results that emerge from these requirements. A traceable link should exist between user needs, design inputs, design outputs, and the associated verification and validation evidence.
Are instructions for use a design output?
Yes. The instructions for use are a documented development result and contain information on the safe and proper use of the product. They therefore typically count among the design outputs. They should not, however, automatically be understood as the preferred risk control measure. Where possible, use-related risks should first be reduced through an inherently safe design of the user interface.
Do design inputs and outputs have to be formulated in measurable terms?
Design inputs must be formulated so unambiguously and verifiably that their implementation can be verified. Design outputs must be sufficiently concrete and documented to allow their conformity with the design inputs to be assessed. Not every requirement has to be formulated exclusively in quantitative terms, but there must be an objective and traceable procedure for assessing its fulfillment.
What is the difference between verification and validation?
Design verification checks whether the design outputs meet the specified design inputs. Design validation checks whether the resulting medical device meets the user needs and the requirements of the intended application. It is performed on the product or on representative product units under defined and, where possible, representative conditions of use.
Do you want to derive usability-relevant design inputs systematically from user research, the use specification, and the use-related risk analysis, and translate them traceably into design outputs? We support you throughout the usability engineering process according to IEC 62366-1.
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
- ISO 13485:2016, Medical devices, Quality management systems, Requirements for regulatory purposes
- 21 CFR Part 820, Quality Management System Regulation (QMSR)