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Problem

Although sites may adhere to accessibility recommendations, users may still experience navigational problems. This is partly due to the fact that Web pages are increasingly designed for parallel or non-serial navigation, offering a variety of options within one page (frames, tables, drop down menus etc). Complex Web pages and parallel design can cause problems for users who are navigating the site using assistive technologies. Our approach is aimed at focusing on the main difficulties encountered by the visually impaired when they interact with graphical user interfaces through a screen reader or a magnifier. In the specific case, we concentrated on the interaction with Web sites.
The main navigational problems that can arise when using a screen reader or magnifier are lack of context, information overload, and excess of information sequential reading. Our investigation attempts to address these usability problems by structuring and organizing the content and UI elements in order to allow for better interaction through screen readers and an adequate layout as well.

Definition

In order to make Web sites more accessible and usable, we identified 15 criteria. For each criterion one or more checkpoints must be applied:

• Criteria are general principles intended for Web site developers and designers. Such principles should be followed to improve accessibility and usability of Web sites, especially for users who navigate through screen reader.
• Checkpoints are technical solutions that allow the application/evaluation of the proposed criteria. Each criterion is defined by one or more checkpoints.

CLASSIFICATION

In a first approach, the criteria were grouped in three sets according to three main usability principles. Next, they are also classified and grouped according to four logical dimensions based on general issues which should be taken into account during design of Web sites.

Hence, criteria are classified as follows:

• on the bases of the main aspects of usability involved, criteria are assigned to three different groups: effectiveness, efficiency, and satisfaction;
• depending on the type of impact on the user interface, criteria are classified and grouped according to four logical dimensions based on general issues which should be taken into account during design of Web sites: structure and arrangement, content appropriateness, multimodal output, and consistency.

EVALUATION

Our criteria can be used to evaluate Web site usability/accessibility. Two complementary approaches can be combined:

• Expert testing (inspection evaluation). A competent tester (confident with criteria) examines several Web sites and checks if and to what extent criteria have been applied by developers.
• User testing. Blind/low vision users test the impact of criteria on web navigation: they are asked to perform assigned tasks while navigating two versions of the same web site, with and without criteria. For each user, the time required to accomplish tasks in the two cases is recorded. The time difference is used as indicator of the influence of criteria on navigation

Our criteria were used for a preliminary evaluation, to test their validity and control if their application could actually improve blind users' navigation.

• The expert testing (inspection evaluation) revealed that, within tested Web sites, the majority was not sufficiently usable.
• The user testing revealed that the application of our criteria significantly reduced the navigation time required to accomplish several types of tasks.