Design in practice practice questions.

A hospital ward is buying overbed tables for patients who eat sitting up in bed. The patients range from small older women to tall adult men, and each table stays with one patient for several days. Which approach to the table height gives the best fit for this user population?

• Fixed at the 50th percentile seated elbow height
• Fixed at the 95th percentile seated elbow height
• Adjustable from the 5th to the 95th percentile seated elbow height
• Fixed at the 5th percentile seated elbow height, with a cushion supplied for taller patients

Answer: Adjustable from the 5th to the 95th percentile seated elbow height

Where one product must serve a wide spread of body sizes and stays with each user long enough to be set up, adjustability across the 5th to 95th percentile range is the standard user-centred solution. Any fixed value, including the 50th percentile, leaves a large part of the population working at the wrong height.

A primary school orders one design of coat hook rail for a corridor used by pupils aged 4 to 11 and by the adults who tidy the corridor at the end of the day. The pupils hang and collect their own coats twice a day, the adults handle the coats for a few minutes after the pupils have gone home, and only one rail height can be fitted. Which decision best fits this situation?

• Fit the rail at the height that suits the adults who tidy the corridor
• Fit the rail at the height the youngest pupils can reach unaided
• Fit the rail midway between the comfortable heights of the two groups
• Fit the rail at the height the oldest pupils can reach unaided

Answer: Fit the rail at the height the youngest pupils can reach unaided

The decision is settled by which group cannot compensate: the adults can work at any height below their own and are there only briefly, while the youngest pupils use the rail unsupervised every day and simply fail if it is too high. A compromise height or an adult height leaves the smallest users dependent on help, which is the outcome the rail is meant to prevent.

A team must show that its redesigned railway ticket machine is more usable than the machine it replaces. During the trial they log, for each participant, the time taken per completed purchase as their measure of efficiency, and separately the number of wrong button presses. Which usability attribute does the count of wrong button presses measure?

• Effectiveness - the accuracy and completeness of task achievement
• Efficiency - the effort and time used to complete the task
• Satisfaction - how comfortable and positive users feel when using it
• Learnability - how quickly a first-time user succeeds unaided

Answer: Effectiveness - the accuracy and completeness of task achievement

Errors describe whether the task was carried out correctly, which is effectiveness; the recorded times measure efficiency. Learners commonly merge the two, but a machine can be fast and still lead users to buy the wrong ticket.

A team maps the grip pressure exerted on a screwdriver handle by ten users. The map shows a peak of 210 kPa on the palm where a narrow moulding ridge runs along the handle, while the rest of the contact area stays below 60 kPa. Which ergonomic problem do these data identify?

• A handle diameter below the 5th percentile grip diameter
• A coefficient of friction too low for a secure grip
• Insufficient handle length for a full power grip
• A localised pressure hotspot on the palm

Answer: A localised pressure hotspot on the palm

A narrow ridge concentrates the same hand force onto a small contact area, so the local pressure rises and the user feels pain before the tool has been used for long. The data say nothing about grip diameter, friction or handle length, which would show as a different pattern.

A team designing a hospital appointment booking system has interview notes from 31 patients. Before any ideation, the team condenses these notes into three named fictional users, each with stated goals, abilities and frustrations. What is the main purpose of doing this at this point in the project?

• To replace the need for user testing later in the project
• To keep design decisions anchored to concrete user goals
• To provide statistically valid data on the user group
• To record the exact body dimensions of the target population

Answer: To keep design decisions anchored to concrete user goals

Personas turn scattered research into a small number of memorable user profiles that the team can design against and argue with during ideation. They summarise qualitative research, so they neither carry statistical validity nor remove the need for later trials with real users.

A start-up buys a batch of low-cost humidity sensors, designs a self-watering plant pot around them and launches the pot without ever speaking to a gardener. Which element of a user-centred design process has been omitted?

• Identification of user needs in a real context
• Generation of alternative concepts
• Manufacture of a functional prototype
• Preparation of a costed bill of materials for production

Answer: Identification of user needs in a real context

User-centred design starts from an observed need in the users' own context, not from a component that happens to be available. Concepts, prototypes and costings can all be produced by a technology-driven team and are therefore not what is missing here.