Resources on Accessible/Universal Design Principles and Performance Measures

Accessibility addresses the ability to access the intended use of a product or service for which there is benefit. This includes, of course, persons with disabilities. There are degrees of access to a product or service, both at the level of the individual (e.g., use may be somewhat difficult, difficult, impossible without assistance, impossible; inaccessible components or features may be optional or essential) and the level of the population (e.g., more difficult or impossible for certain groups of users). Our R3 (Accessibility Metrics) project is developing measurement tools to determine degrees of accessibility for categories of medical instrumentation.

While there is often synergy between accessibility and usability (extent to which a product can be used by specified users to achieve specified goals in an effective and efficient manner, to the satisfaction of these users), accessibility focuses on minimizing access barriers (often with a focus on promoting accessible design features) rather than ability to use (often with a focus on task analysis).

Universal usability, or ability to use by all, is another commonly used term that focuses on the vision of designing products so that they are usable by the widest range of people operating in the widest range of situations as is practical. Universal access, or ability to access by all, is another commonly used term, with a variety of meanings depending on the context. Generally it includes usability but also access across other barrier domains, such as distance and economic status.

At times making an interface more fully accessible may lower the degree of usability for some people. For instance, an interface may appear more complex when multimodal options are added that make it accessible to more people. Multimodality refers to support for transformations to alternative sensory interface modes for a channel (e.g., between text and speech), such that more than one modality is available to access content. Multimodal interfaces are often necessary for a product or service to be accessible.

Accessible design targets removing barriers that prevent individuals from participating in the use of a product, i.e. extending a design to maximize the number of potential customers who can readily use the device or service. Thus accessible design maximizes the accessibility of a product. There are two basic strategies for enhancing access through design: direct access (direct adaptations to product designs that significantly improve their accessibility) and assistive access (product interfaces that enable an add-on assistive technology to provide the user with full access). Legislation such as Section 508 of the Rehab Act allows either strategy. For many types of products there is legislation that defines and mandates product accessibility, often supported by published standards and guidelines for its implementation (e.g., by the U.S. Access Board). This provides a pragmatic delineation between Accessible Design (often mandated) and Universal Design (a principle/process). From this perspective Accessible Design can be defined as the design of entities that satisfy specific legal mandates, guidelines, or code requirements with the intent of providing accessibility to the entities for individuals with disabilities. THis definition is limited, however, especially as related to products: the legal standards and codes do not span the landscape of products simply because the existing laws do not span this range. For instance, the Access Board's accessibility guidelines target three core areas: the built environment, transportation, and electronic and information technologies (E&IT). Furthermore, a product and its design can have degrees of accessibility, and indeed RERC-AMI Program R3 Accessibility Metrics is working on scoring the degree of accessibility of products.

There are many resources that address accessibility and accessible design, including a number on the Web:

A good reference from the engineering academic community is Erlandson RF and Babbitt BC (2001), "The Movement of Accessible Design Principles into Mainstream Engineering: Now and Then," in Emerging & Accessible Telecommunications, Information & Healthcare Technologies, Winters JM, Robinson C, Simpson R & Vanderheiden G., eds, pp. 2-18, RESNA Press, Arlington. (Note: if a project design supervisor would like a free copy of this book, which includes many other chapters related to accessibility and design, send an email with mailing address to jack.winters@mu.edu.)

Universal Design is the design of products and environments to be effectively and efficiently usable by people with a wide range of abilities, to the greatest extend possible, without the need for adaptation or specialized design. It clearly relates to usability and accessibility, and shares some common ground with the concepts of Universal Usability (ability to use by all) and Universal Access (ability to access by all).

Here is a consensus European version:

"Universal design is a strategy, which aims to make the design and composition of different environments and products accessible and understandable to as well as usable by everyone, to the greatest extent in the most independent and natural manner possible, without the need for adaptation or specialized design solutions." (Council of Europe Committee of Ministers, 2001)

Designers should be especially cognizant of the Principles of Universal Design (available as pdf), as developed through the Center for Universal Design by a working group in 1997 (Story, 1998; Story and Mueller, 2002):

  1. Equitable Use
  2. Flexibility in Use
  3. Simple and Intuitive Use
  4. Perceptible Information
  5. Tolerance for Error
  6. Low Physical Effort
  7. Size and Space for Approach and Use

These principles were developed for both the built environment and product design. Since our focus is on product design, it is instructive to consider, next to each principle, more pragmatic performance measures. The following table includes both the original consensus guidelines from the working group (left column) and field-tested usable product design concepts, for your consideration. Of note is that many of these cannot always be fully achieved, and the considerations within the table below often can't be answered with a "yes" or "no" but have a degree of truth on a continuum. But they are worth striving for.

Universal Design: Principles & Performance Measures

[adapted from Story and Mueller (2002)]
Principles Performance Measures for Products
Principle One - Equitable Use: The design is useful and marketable to people with diverse abilities
Provide the same means of use for all users; identical whenever possible; equivalent when not. All potential users could use this product in essentially the same way, regardless of differences in personal capabilities.
Avoid segregating or stigmatizing any users. Potential uses could use this product without feeling segregated or stigmatized because of differences in personal capabilities.
Make provisions for privacy, security, and safety equally available to all users. Potential users of this product have access to all features of privacy, security, and safety, regardless of personal capabilities.
Make the design appealing to all users. This product appeals to all potential users.
Principle Two - Flexibility in Use: The design accommodates a wide range of individual preferences and abilities
Provide choice in methods of use. Every potential user can find at least one way to use this product effectively.
Accommodate right- or left-handed access and use. This product can be used with either the right or left had alone.
Facilitate the user's accuracy and precision. This product facilitates (or does not require) user accuracy and precision.
Provide adaptability to the user's pace. This product can be used at whatever pace (quickly or slowly) the user prefers.
Principle Three - Simple and Intuitive Use: The design is easy to understand, regardless of the user's experience, knowledge, language skills, or current concentration level
Eliminate unnecessary complexity. This product is as simple and straightforward as it can be.
Be consistent with user expectations and intuition. An untrained person could use this product without instructions.
Accommodate a wide range of literacy and language skills. Any potential user can understand the language used in this product.
Arrange information consistent with its importance. The most important features of this product are the most obvious.
Provide effective prompting and feedback during and after task completion. This product provides feedback to the user.
Principle Four - Perceptible Information: The design communicates necessary information effectively to the user, regardless of ambient conditions or the user's sensory abilities.
Use different modes (pictorial, verbal, tactile) for redundant presentation of essential information. This product can be used without hearing.
Maximize "legibility" of essential information. This product can be used without sight.
Differentiate elements in ways that can be described (i.e., make it easy to give instructions or directions). The features of this product can be clearly described in words (e.g., in instruction manuals or on telephone help lines).
Provide compatibility with a variety of tech niques or devices used by people with sensory limitations. This product can be used by persons who use assistive devices (e.g., eyeglasses, hearing aids, sign language, or service animals).
Principle Five - Tolerance for Error: The design minimizes hazards and the adverse consequences of accidental or unintended actions.
Arrange elements to minimize hazards and errors: most used elements, most accessible; hazardous elements eliminated, isolated, or shielded. Product features are arranged according to their importance.
Provide warnings of hazards and errors. This product draws the user's attention to errors or hazards.
Provide fail safe features. If the use makes a mistake with this product, it won't cause damage or injure the user.
Discourage unconscious action in tasks that require vigilance. This product prompts the user to pay attention during critical tasks.
Principle Six - Low Physical Effort: The design can be used efficiently and comfortably and with a minimum of fatigue.
Allow user to maintain a neutral body position. This product can be used comfortably (e.g., without awkward movements or postures).
Use reasonable operating forces. This product can be used by someone who is weak or tired.
Minimize repetitive actions. This product can be used without repeating any motion enough to cause fatigue or pain.
Minimize sustained physical effort. This product can be used without having to rest afterward.
Principle Seven - Size and Space for Approach & Use: Appropriate size and space is provided for approach, reach, manipulation, and use regardless of user's body size, posture, or mobility.
Provide a clear line of sight to important elements for any seated or standing user. It is easy for a person of any size to see all the important elements of this product from any position (e.g., standing or seated).
Make reach to all components comfortable for any seated or standing user. It is easy for a person of any size to reach all the important elements of this product from any position (e.g., standing or seated).
Accommodate variations in hand and grip size. This product can be used by a person with hands of any size.
Provide adequate space for the use of assistive devices or personal assistance. There is enough space to use this product with devices or assistance (e.g., wheelchair, oxygen tank, or service animal).

Story, M.F. (1998) Assessing usability: The principles of universal design. Assistive Technology, 10:4-12.

Story, M.F. and Mueller, J., (2002) Universal Design Performance Measures for Products: A Tool for Assessing Universal Usability, in Emerging and Accessible Telecommunications, Information and Healthcare Technologies (Winters, J.M., Robinson, C.J., Simpson, R.C. and Vanderheiden, G.C., eds.), pp. 19-28, RESNA Press, Arlington.

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