| Summary: | Being able to use websites is an important aspect of every-day life to most people, including disabled people. However, despite the existence of technical guidelines for accessibility for more than a decade, disabled users still find problems using websites. However, our knowledge of what problems people with disabilities are encountering is quite low. The aim of the work presented in this thesis was to conduct a study that characterises the problems that print-disabled users (blind, partially sighted, dyslexic users) are encountering on the web. This characterisation includes the categorisation of user problems based on how they impact the user. Further, frequency and severity of the main types of problems were analysed to determine what were the most critical problems that are effecting users with print-disabilities. A secondary goal was to investigate the relationship between user-based measures of accessibility and measures related to technical guidelines, especially the Web Content Accessibility Guidelines (WCAG) 1.0 and 2.0 from the World Wide Web Consortium (W3C). This was done to both identify gaps in the current guidelines, as well understanding where technical guidelines are currently not sufficient for addressing user problems. The study involved task-based user evaluations of 16 websites by a panel of 64 users, being 32 blind, 19 partially sighted and 13 dyslexics and manual audits of the conformance of websites to WCAG 1.0 and 2.0. The evaluations with print-disabled users yielded 3,012 instances of user problems. The analysis of these problems yielded the following key results. Navigation problems caused by poor information architecture were critical to all user groups. All print-disabled users struggled with the navigation bars and overall site structure. Blind users mentioned problems with keyboard accessibility, lack of audio description of videos and problems with form labelling often. However, beyond these seemingly low-level perception and execution problems, there were more complex interaction problems such as users not being informed when error feedback was added dynamically to a page in a location distant from the screen reader. For partially sighted users, problems with the presentation of text, images and controls were very critical, especially those related to colour contrast and size. For dyslexic users, problems with language and lack of search features and spelling aids were among the most critical problems. Comparisons between user problems and WCAG 1.0 and WCAG 2.0 did not show any significant relationship between user-based measures of accessibility and most measures based on technical guidelines. The comparisons of user problems to technical guidelines showed that many user problems were not covered by the guidelines, and that some guidelines were not effective to avoid user problems. The conclusions reinforced the importance of involving disabled users in the design and evaluation of websites as a key activity to improve web accessibility, and moving away from the technical conformance approach of web accessibility. Many of the problems are too complex to address from the point of view of a simple checklist. Moreover, when proposals are made for new techniques to address known user problems on websites, they must be tested in advance with a set of users to ensure that the problem is actually being addressed. The current status quo of proposing implementations based on expert opinion, or limited user studies, has not yielded solutions to many of the current problems print-disabled users encounter on the web.
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