User-centred design (UCD).

Principles of UCD

• Take full account of the users, the task being performed and the relevant environment.
• Involve users during design and development rather than waiting until the finished product is evaluated.
• Refine the design through user-centred evaluation and an iterative design process.
• Consider the whole user experience, including comfort, ease of use, safety and interaction.
• Use a multi-skilled, multidisciplinary team where appropriate, including product designers, engineers, industrial designers, ergonomists and sales or marketing specialists.

Investigating users

Designers need evidence about users' needs, wants and values. Physical needs can vary with age, mobility, disability and other user characteristics. Emotional needs concern preferences, aspirations and what users like or dislike. Designers may also need to consider intellectual needs and wider social or environmental values.

• Questionnaires and surveys can collect information such as age, interests and shopping habits and help explain why consumers choose one product over another.
• Interviews allow potential users to explain their needs and wants in greater detail.
• Focus groups provide qualitative feedback from panels of potential customers.
• Observation shows how people actually use products and can reveal ergonomic problems that users may not describe themselves.
• Empathic research or immersion allows designers to experience or simulate user limitations such as restricted mobility.
• Product analysis and disassembly can identify useful features, materials, components and construction methods in existing products.

Anthropometrics

Anthropometrics is the study and measurement of human body dimensions. Designers use anthropometric data to decide dimensions such as seat height, reach distance, clearance, handle size and working height.

Measurements vary between people, so data is commonly presented using percentiles. The 5th percentile represents a relatively small user and the 95th percentile a relatively large user. The percentile chosen depends on the design problem: clearance dimensions generally need to accommodate larger users, while reach dimensions may need to accommodate smaller users. Adjustable products can accommodate a wider range.

For a bespoke product, anthropometric measurements may be taken directly from the intended user rather than relying only on population data.

Ergonomics

Ergonomics is the study of how people interact with products and their working environment. Designers consider posture, grip, force, reach, visibility, control layout, feedback, repetitive movement and physical effort to improve comfort, safety and ease of use.

Anthropometrics = human measurements.
Ergonomics = how effectively and comfortably the user interacts with the product and environment.

Task analysis and user testing

Task analysis involves observing users carrying out specific tasks with an existing product or prototype. It can identify difficulties, inefficient movements, confusing controls or physical strain. The findings should then be used to modify the design and tested again.

User testing is most valuable when it reflects the intended context of use. A design that works in a workshop demonstration may behave differently when used by its real target group in its normal environment.

Inclusive and empathic design

Inclusive design aims to make products accessible to the widest practical range of people, including children, older users and people with disabilities. Empathy helps the designer understand restrictions that may otherwise be overlooked.

For example, designers can simulate restricted movement, reduced grip or impaired vision to understand the difficulties faced by less mobile users. The resulting evidence may affect handle shape, control size, force required, visibility or access.

Using user evidence

User-centred design is not simply asking users what they like. Designers must interpret research and decide how it affects the proposal. A change that improves comfort for one user group may increase size, cost or complexity, so decisions need to balance user evidence with the specification and other design constraints.