Framework

This section introduces a framework for relating data regarding user capabilities to descriptions of products and their interfaces. It acts as an introduction to seven further sections describing capabilities particularly relevant to product interaction.

When reviewing the capability demands associated with using a particular product it is important to consider all seven categories since many people, especially those in older age groups, experience more than one capability loss in the form of multiple minor impairments.

On this page:

Any interaction with a product or service typically requires a cycle where the user

• Perceives
• Thinks
• Acts

Perceiving and acting both require sensory and motor capabilities. In addition, the body's sensory and motor resources are controlled by the brain and therefore require cognitive capability.

For example, perceiving text on a product can rely on the hands to move and orientate the product for visual examination or the eyes could guide the fingers to press particular buttons. However, for the most part, perceiving requires sensory capability, thinking requires cognitive capability, and acting requires motor capability.

The interaction between a product and the user’s capabilities is also influenced by the environment in which the product is used. For example, low, or indeed high, ambient light levels can compromise a user’s ability to read.

The following seven capability categories are helpful to measure a person's capability, or assess the ability level that a product demands in order to use it.

• Vision is the ability to use the colour and brightness of light to detect objects, discriminate between different surfaces, or the detail on a surface
• Hearing is the ability to discriminate specific tones or speech from ambient noise and to tell where the sounds are coming from.
• Thinking is the ability to process information, hold attention, store and retrieve memories and select appropriate responses and actions.
• Communication is the ability to understand other people, and express oneself to others (this inevitably overlaps with vision, hearing, and thinking).
• Locomotion is the ability to move around, bend down, climb steps, and shift the body between standing, sitting and kneeling.
• Reach & stretch is the ability to put one or both arms out in front of the body, above the head, or behind the back.
• Dexterity is the ability of one or both hands to perform fine finger manipulation, pick up and carry objects, or grasping and squeeze objects.

Sensory capability includes vision and hearing. Cognitive capability includes thinking and communication. Motor capability includes locomotion, reach & stretch and dexterity.

The 1996/97 Family Resources Survey was commissioned by the UK government to provide statistics about households in Great Britain. In the same years, the Disability Follow-up to the Family Resources Survey was performed in order to help plan welfare support for disabled people.

People were selected for the Disability Follow-up Survey if they met certain criteria, such as being in receipt of incapacity benefit. Approximately 7500 participants were asked up to 300 questions regarding whether they were able to perform certain tasks such as

"Can you see well enough to read a newspaper headline?"

The results were collated to provide estimates for the national prevalence of disability. This survey is the most recent to consider all seven capability categories, and is therefore the only source suitable for considering multiple capability losses. According to the definition used in the survey, 17.8% of the GB adult population have less than full ability in one or more categories. The GB adult population was 45.6 million people at the time of the survey.

The following pages explore further details of the disability survey, followed by the prevalence data and definitions of full ability for: Sensory capabilities, Cognitive capabilities, and Motor capabilities.

The questions within the Disability Follow-up Survey can be used to estimate the number of people that would be unable to perform a certain task that is required to use a product, and would therefore be excluded.

The 300 survey questions were combined to form ability levels that could measure quality of life impairment, often using multiple questions to create each level. However, the manner in which the questions were combined can make the levels difficult to interpret for product interaction.

Further research will create more useful scales from the original survey questions, and specifically collect additional capability data for the purpose of calculating exclusion. Until then, the Disability Follow-up Survey remains the best source of coherent data for estimating design exclusion.

Sensory capability describes the combination of vision and hearing capabilities. The Disability Follow-up Survey found that 8.7% of the GB adult population have less than full ability in one or both of these categories. The GB adult population was 45.6 million people at the time of the survey.

A person with full vision ability can see well enough to

• Recognise a friend across the road without difficulty
• Read ordinary newsprint without difficulty

A person with full hearing ability can hear well enough to:

• Follow a conversation during background noise without great difficulty
• Follow a TV programme at a volume that others find acceptable

Cognitive capability describes the combination of thinking and communication capabilities. The Disability Follow-up Survey found that 5.7% of the GB adult population have less than full ability in one or both of these categories. The GB adult population was 45.6 million people at the time of the survey.

A person with full thinking ability can perform tasks such as

• Hold a conversation, without losing track of what is being said
• Write a short letter to someone without help
• Count well enough to handle money
• Remember a message and pass it on
• Remember the names of friends and family that are seen regularly

A person with full communication ability can

• Communicate with strangers with no difficulty

Each person's thinking ability was measured by counting up the number of everyday tasks they were unable to perform. This approach does not relate to cognitive science which makes it particularly challenging to interpret the results in terms of product exclusion.

Motor capability describes the combination of locomotion, reach & stretch, and dexterity capabilities. The Disability Follow-up Survey found that 14.7% of the GB adult population have less than full ability in one or both of these categories. The GB adult population was 45.6 million people at the time of the survey.

A person with full locomotion ability can:

• Walk 350 metres (≈ 400 yds) without stopping
• Ascend/descend a flight of 12 steps without handrails and without resting
• Bend down to use a dustpan and brush and then straighten up again

A person with full reach & stretch ability can

• Raise both arms out in front, up to the head, or behind the back

A person with full dexterity ability can

• Tie a bow in laces with no difficulty
• Pick up and carry a 2.5 kg bag of potatoes in each hand
• Squeeze a sponge with each hand

The Disability Follow-Up Survey only measured reach & stretch relative to the person's own body, so it is not possible to convert this to standard measurements like "can reach to 2.0 metres".

The results from the Disability Follow-up Survey were presented in terms of the number of people with specific levels of disability. For vision, level V1 refers to extreme disability, V9 is mild disability, and V10 is full vision ability.

For the purpose of inclusive design, it is more useful to consider V1, V2 and V3 as being increasing levels of vision ability. For example, those in ability level V3 can tell by the light where the windows are (opposite of V1), and they can see the shapes of furniture in a room (opposite of V2), but they cannot recognize a friend if close to his face.

In order to estimate design exclusion, it is necessary to sum together the ability bands, to work out the total number of people who would be unable to perform a specific task.

For example, supposing a product required the user to see well enough to read a newspaper headline. The number of people excluded would be the sum of people in categories V1-V5, which is approximately 1% of the GB adult population.

However, if the required task is not specifically mentioned on the scale, then some judgment will be required to position the task between existing ability levels. The next page shows the same data presented in a suitable format to achieve this.

The data from the Disability Follow-Up Survey can also be presented in a format suitable for assessing design exclusion directly, where the ability level that a product demands in order to use it is directly plotted against the number of people who will be excluded.

For example, with regard to vision demand, approximately 1% of the GB adult population would be excluded from a product that requires the user to see well enough to read a newspaper headline.

The Disability Follow-Up Survey does not make any reference to the environment, or to fatigue caused by repeated actions. Until better data is obtained, these factors can only be accounted for by using judgement to modify the demand level appropriately

Estimating the number of people who would be unable to use a product based on multiple different capability demands requires an Exclusion calculator, such as the one within the Inclusive design tools section on this website.

Within each capability section, guidance is provided to help design products and services that are more usable by people who are impaired in that capability.

The guidance provides suggestions and highlights issues that need to be considered, but is not a set of rules to be strictly followed, nor a list of items that can be 'checked' to guarantee a successful and inclusive design. The advice works effectively within the context of an inclusive design process, as elaborated within the How to get started section.

Successful application of the design guidance requires understanding the needs and characteristics of the target users, developed through a discovery phase at the start of the design process.

The design guidance should also be supplemented by consultation with experts in the relevant capabilities and with users who have capability losses. Such consultation enables the guidance to be better interpreted, and can evaluate whether capability range of the target users matches appropriately with the demands made by the product or service.

For more information on using design guidance, see Nicolle and Abascal (2001).

Nicolle and Abascal (2001) Inclusive design guidelines for HCI. Taylor and Francis, London UK.

The principles of demand and exclusion can be used to estimate the number of people who would be unable to use the kettle shown opposite. For the sake of simplicity, the results only consider vision and dexterity.

The tasks required to use the kettle are identified as: separate kettle from power source, carry to water source, fill the kettle to desired level, re-attach to power source, switch on, and finally, pour the boiling water into mug. The level of design exclusion for an ideal kettle would be no greater than the number of people who would be unable to pick up and drink hot liquid from a mug, which is also analysed for comparison.

The revised capability scales were used to assess the demand level for the tasks required to use each product, then the Exclusion calculator (within Inclusive design tools) was used to estimate the proportion of the population that would be unable to perform these tasks.

The combined number of people excluded from using the kettle (7.0%) is less than the total for each separate capability (6.5 + 0.9 = 7.4%), because some people have both low dexterity and vision capability, but are counted only once in the combined exclusion estimate.