Authors: Dr. Sam Waller, University of Cambridge, Engineering Design Centre and Prof. P John Clarkson, University of Cambridge, Engineering Design Centre. Edited by James Hubbard, Senior Design Advisor, Products and Services, Centre for Excellence in Universal Design, NDA; Dónal Rice, Senior Design Advisor, ICT, Centre for Excellence in Universal Design, NDA
When proposing or writing policies to improve the extent to which products enable people in a society to live independently and participate fully in all aspects of life, careful consideration should be taken of the impact of this legislation on the existing balance between utility, usability, accessibility, desirability, affordability, viability and compatibility. For example, mandatory legislation that increases the production costs of a product will reduce its sales volume, which reduces its viability for the business and therefore limits the potential real-world uptake. Each of these characteristics is now described in more detail:
Utility is the extent to which the product provides functionality that meets real user needs, such as those associated with independent living and participation in society
Usability is the extent to which the product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction, in a specified context of use
Accessibility is the extent to which the product is usable by people with the widest range of capabilities
Desirability is the extent to which ownership and use of the product leads to pleasure and satisfaction
Affordability is the extent to which the perceived value of the product is greater than its perceived cost to the users, given their available income
Viability is the extent to which the sale and maintenance of the product achieves success for the corresponding company
Compatibility is the extent to which the product works together with other devices, and conforms with current technical standards, guidelines and laws.
The focus on utility, usability, accessibility, desirability, affordability, viability and compatibility draws together best practice from the population-based ethos of inclusive design, governing principles of usability, and the definitions of accessibility and usability within ISO 9241.
Considering utility is an appropriate starting point, as the primary purpose of most products is to offer some kind of benefit to the user (note that utility focuses on the benefit, rather than the number of features). Usability refers to the extent to which users can access the utility of the product, and are satisfied with the experience of doing so. When testing the usability of a product, the users considered are typically fully able, and selected to reflect the majority perspective of the target market.
Testing the accessibility of a product is typically based on the similar underlying principles as usability testing, but focusing on users with some kind of impairment. The combination of usability/accessibility can therefore reflect the extent to which an entire population of people can access the utility of a product, and are satisfied with the experience of doing so. In this sense, "users" becomes analogous to "all the potential customers", and people with impairments are accounted for based on the prevalence of those impairments within the target market.
The utility, usability and accessibility of a product influence the extent to which it is desirable to own, although other factors affecting desirability also include aesthetics, social and cultural factors.
The perceived value of a product often reflects a combination of its utility, usability/accessibility and desirability. Furthermore, the product's affordability to the user depends on the perceived costs of purchasing, transporting, and maintaining it, together with the perceived value and the available income. Also related to affordability, the sale price of the product, sales volume, production costs and support costs will influence the viability of the product for the corresponding company.
Finally, the product's compatibility with other devices may form a crucial part of enabling people to live independently and participate fully in all aspects of life; a classic example being compatibility problems between remote controls for televisions, set-top boxes, DVD players and video recording devices. Compatibility (also known as interoperability) is especially significant when assistive devices might be used together with the product; this compatibility is often arranged by ensuring that both the product and assistive devices conform to technical standards. Compatibility with current laws, guidelines, traditions and expectations will also affect real-world uptake. Note that compatibility is time dependent, and typically evolves between past, present and future.
Utility, usability, accessibility, desirability, affordability, viability and compatibility may be seen as a framework of design requirements for a product that will help to enable people to live independently and participate fully in all aspects of life. The next sections explore how Universal Design can produce products that successfully meet these requirements.