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When Links Change: How Additions and Deletions of Single Navigation Links Affect User Performance

Lauren F.V. Scharff and Philip Kortum

Journal of Usability Studies, Volume 5, Issue 1, Nov 2009, pp. 8 - 20

Article Contents


Introduction

The Web has evolved into an important tool in everyday modern life (Haythornthwaite & Wellman, 2002). From the sharing and gathering of information to the business of e-commerce, typical users visit hundreds of pages every week (Hawkey & Inkpen, 2005). Even though the content of all these pages is as varied as the interests of the users who seek them out, each of these pages shares a common elementólinks. While some pages are simply a collection of links, or links imbedded in content, most pages employ some common, persistent collection of links that are collectively referred to as navigation links. In western language Web sites, navigation links are generally located near the top and left of Web pages (Weinreich, Obendorf, Herder, & Mayer, 2006) and serve to guide the user to the content of interest on any given site.

Because the Web was designed to easily share information, it is constantly changing. New pages are added, old pages are taken down, and content is continually modified. Over the course of 3 years, the number of new sites added to the Internet more than doubled to 108 million (Netcraft, 2006). Almost 40% of the pages on the Web are changed in some way over the course of a week, with 23% being changed daily (Cho & Garcia-Molin, 2000). This degree of change is not surprising, as these measures included changes to content, and many of the most popular sites are those used to shop or gather frequently updated news information (Adar, Teevan, & Dumais, 2008). While changes to the content of a site may be beneficial to users, changes to the navigational links used to access that content can prove to be more problematic, especially when considering that approximately 53% of visits to Web pages are repeat visits (Tauscher & Greenberg, 1997). Kohler (2002) found that over a 1-year period approximately 18% of Web pages undergo changes in which links are renamed or deleted. Over a 4-year period the number of pages undergoing this kind of change rises to nearly 39%. Adding links to pages is less common, with approximately 8% of the Web pages adding links over the course of a year, with this number increasing to 30% over 4 years.

How do these changes impact users? It is known that changes to user interfaces can have detrimental impacts on users (Tamborello, Chung, & Byrne, 2008). It is also known that wholesale changes to Web sites (site redesigns) adversely impact user performance, at least in the short term (Jones, Farris, & Johnson, 2005). Even if an old site had significant usability issues associated with navigation, there will be some degree of relearning involved for users who had previously used the site in its original form. Often times, however, site navigation does not change as part of a complete redesign. Rather, in the course of normal maintenance and content update, small navigation changes are implemented. What are the impacts of these smaller changes? Changing a single, crucial link may be a more significant issue than changing a large number of rarely used navigation links.

Consistency of navigation is one of the design elements that is supported by the leading evidence-based Web design guidelines, such as the U.S. Department of Health and Human Services Research based Guidelines (2006). This design recommendation is almost always present even when overall Web design guideline agreement tends to be low (Bevin, 2005). However, one of the difficulties in trying to maintain navigation consistency is trying to decide when a change in the navigation structure is enough to be considered major.

Scharff (2006) demonstrated that there were indeed performance decrements when a single pertinent link was removed from the navigational structure. Scharff had users look for a piece of target information in the first visit to a site and then had them repeat the task immediately following completion of this first task. There were four conditions: two consistent conditions in which the pages presented were identical across visits and the pertinent link was either always present or always absent, and two inconsistent conditions in which the link was either present then absent or absent then present. In all cases, the information could be found using other navigational paths that were three clicks in length. Her results showed that users generally took longer to find the information and searched more pages in the condition where the link was present on the first visit and absent on the second. Overall, the addition of the pertinent link in the inconsistent condition improved user performance, due to a subset of users who noticed the added link and used it to directly navigate to the target page. The time between the first and subsequent visit was extended to one week in a subsequent study by Kortum and Scharff (2007) and the results were similar. These results suggest that even a single visit to a site can establish relatively long-lasting path memories in users that will impact their behaviors on subsequent visits to a site.

Because users may visit certain kinds of sites consistently but infrequently, it could be that changes to navigational structures have less impact than these earlier studies might suggest if the time between visits is longer than those previously studied and memory of the navigational structure has faded. This paper extends the previous work by including longer times between a userís first and subsequent visits to a site. We describe the results of an experiment in which an important link in the main navigational menu was altered by adding or deleting a single link in between a userís first and subsequent visits. The length of time between the first and second visit varied from an immediate revisit to as long as three weeks.

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