Accessibility in User-Centered Design: Evaluating for Accessibility
A key aspect of successful User-Centered Design (UCD) is evaluating early and throughout the UCD process. The Background: Accessibility & User-Centered Design (UCD) chapter introduces the User-Centered Design process.
This section provides information on incorporating accessibility into the following evaluation methods:
- Importance of Comprehensive Accessibility Evaluation
- Standards Review
- Heuristic Evaluation
- Design Walkthroughs
- Screening Techniques
- Usability Testing
"Accessibility Evaluation Tools and Techniques" in the Appendix: Resources lists additional resources on evaluating accessibility, including methodologies focusing on specific product accessibility.
Accessibility evaluation is often limited to assessing conformance to accessibility standards. Conformance to accessibility standards is important: in some cases it's a legal requirement and in others it's just a good way to help check that you've adequately covered the range of accessibility issues. However, when the focus is only on the technical aspects of accessibility, the human interaction aspect can be lost. Usability evaluation methods can assess usable accessibility to ensure that your accessibility solutions are usable by people with disabilities. 
Some designers needing to meet U.S. Section 508 standards chose to provide alternative"modes of operation and information retrieval". However, in some cases where the standard was technically met by providing an alternative, the products were awkward to use or were totally unusable by some people with disabilities. These cases illustrate the importance of going beyond just meeting a minimum accessibility standard without sufficient evaluation.
Effective accessibility evaluation includes both evaluation expertise and the experience of people with disabilities. If you have people with disabilities easily available to help with evaluation, such as employees in the same building, you probably want to do lots of informal evaluation with them on early design prototypes. In the more common case where it takes more effort to get people with disabilities for evaluation, you probably want to employ the other evaluation methods first.
If you have limited budget you might need to do the evaluations yourself, or you might be able to afford an accessibility specialist. An accessibility expert with first-hand experience of how people with different disabilities interact with products can:
- evaluate accessibility issues for a broad range of users, which might not be found by a few individual users in usability testing;
- help fix any known accessibility barriers before bringing in users; and
- focus usability testing or informal evaluation with users on potential areas of concern.
While each evaluation plan will be different based on resources and other factors, ensure that you employ comprehensive evaluation that includes at least a little of the methods described next: standards review, heuristic evaluation, design walkthroughs, screening techniques, and usability testing.
A standards review in the User-Centered Design process assesses whether a product conforms to specified interface design standard. Sometimes the standards are internal style guide recommendations, and other times they are external standards.
Accessibility standards and guidelines are available from international standards organizations; national, state and local governments; industry groups; and individual organizations. The "Standards and Guidelines" section in the Appendix: Resources lists accessibility standards, guidelines, and related articles.
Accessibility standards reviews are often more rigorous than typical user interface reviews, especially when conformance to a standard is a legal requirement. Furthermore, user interface issues often overlap with technical issues in accessibility standards reviews. Specific guidance on accessibility standards conformance is beyond the scope of this book.
Software tools are available to help evaluate web pages and some elements of software. While the tools provide some automated review, human evaluation is still necessary.
Most web accessibility evaluation tools assess how web pages conform to W3C WAI Web Content Accessibility Guidelines (WCAG), and sometimes national standards such as Section 508 Part 1194.22. Most of the tools are commercially available, a few are free, and several have limited functionality available free online. The following resources from WAI cover web accessibility evaluation tools:
- Selecting Web Accessibility Evaluation Tools provides guidance on choosing tools to use to help evaluate Web accessibility. It describes different types, uses, and features of tools.
- Web Accessibility Evaluation Tools is a comprehensive database of over 100 tools in 20 languages.
Although evaluation tools can identify some accessibility issues, evaluation tools alone cannot determine if a product meets standards and is accessible. A good example of what tools can and cannot do is evaluate equivalent alternative (alt) text for images on a web page. Tools can identify images that are missing alt text. However, tools cannot determine if existing alt text is equivalent (that is, does it provide the same information in text as the image provides visually). Judging if the alt text is equivalent requires human evaluation.
Web accessibility evaluation tools can increase the efficiency of evaluation by saving time and effort; however, they cannot replace knowledgeable human evaluators. Rather than thinking of tools as a substitute for human evaluation, think of tools as an aid to human evaluation. 
In a heuristic evaluation,
specialists judge whether each design element conforms to established usability principles.  To conduct a heuristic evaluation for accessibility, accessibility specialists judge whether design elements conform to accessibility principles.
Several resources provide information that can serve as guidance on heuristic evaluation for accessibility:
- Section 255 of the Telecommunications Act, Subpart C: Requirements for Accessibility and Usability is listed in the "Understand the Range of Functional Limitations" section of Design Phase
- Section 508 of the Rehabilitation Act Subpart C -- Functional Performance Criteria is listed below:
§ 1194.31 Functional performance criteria.
(a) At least one mode of operation and information retrieval that does not require user vision shall be provided, or support for assistive technology used by people who are blind or visually impaired shall be provided.
(b) At least one mode of operation and information retrieval that does not require visual acuity greater than 20/70 shall be provided in audio and enlarged print output working together or independently, or support for assistive technology used by people who are visually impaired shall be provided.
(c) At least one mode of operation and information retrieval that does not require user hearing shall be provided, or support for assistive technology used by people who are deaf or hard of hearing shall be provided.
(d) Where audio information is important for the use of a product, at least one mode of operation and information retrieval shall be provided in an enhanced auditory fashion, or support for assistive hearing devices shall be provided.
(e) At least one mode of operation and information retrieval that does not require user speech shall be provided, or support for assistive technology used by people with disabilities shall be provided.
(f) At least one mode of operation and information retrieval that does not require fine motor control or simultaneous actions and that is operable with limited reach and strength shall be provided. 
The purpose of a design walkthrough is to find potential usability problems by
envisioning the user's route through an early concept or prototype.  Typically, a person acts as a representative user while a design team member guides her through actual tasks with early prototypes. Sometimes another team member plays the computer or device, changing paper mockups of windows, drop-down menus, pop-up dialog boxes, and other interface elements.
Ways to incorporate accessibility into design walkthroughs include:
- Focus on specific accessibility issues during regular walkthroughs
- Conduct walkthroughs specifically for accessibility
An example of focusing on specific accessibility issues during regular software walkthroughs is device-independent interaction. The design team listens for the acting user to say,
I would click on this, indicating an action that is completed with a mouse. The team then checks that all actions triggered with a mouse are also available through the keyboard for people who don't use pointing devices. Another example of a specific accessibility issue to evaluate during design walkthroughs is use of sound. When walking through use of a consumer product, the design team listens for the team member playing the device to indicate feedback or interaction provided via sound.
To conduct walkthroughs specifically for accessibility, use personas with disabilities and scenarios that include adaptive strategies to complete the task, as discussed previously in the "Accessibility in Personas" and "Accessibility in Scenarios" sections. For example, the acting user would be blind and another design team member would play the role of the screen reader.
For design walkthroughs of high-fidelity prototypes you can also use Screening Techniques, which are introduced next.
Screening Techniques are simple, inexpensive activities to help identify potential accessibility barriers in product designs. Design teams use screening techniques to learn about accessibility issues and to evaluate prototypes or existing products. Screening techniques save time and money by finding barriers early, when it is less expensive to make changes to the product, and by focusing later usability testing with people with disabilities.
The Screening Techniques section covers screening techniques in more detail.
Usability testing provides quantitative and qualitative data from real users performing real tasks with a product. Usability professionals can evaluate some aspects of accessibility by using standard usability testing protocols, with a few modifications for including participants with disabilities. While usability testing is useful for learning how people use your products and assessing the usability of accessibility solutions, it does not evaluate conformance to accessibility standards.
The following sections discuss usability testing with participants with disabilities:
- Usability Testing
- Henry, S.L. Another-ability: Accessibility Primer for Usability Specialists. Proceedings of UPA 2002 (Usability Professionals' Association annual conference), 2002.
- Henry, S.L. Web Accessibility Evaluation Tools Need People, 2003.
- Nielsen, J. and Mack, R., eds. Usability Inspection Methods. New York: John Wiley & Sons, 1994.
- Architectural and Transportation Barriers Compliance Board. Electronic and Information Technology Accessibility Standards. U.S. Federal Register, 2000.
- Rubin, J. Handbook of Usability Testing. New York: John Wiley & Sons, 1994.