It doesn't take a usability expert to figure out that the visual appearance of an interface is important. In Fogg, Soohoo and Danielson (2002), domain novices report that visual elements such as layout, use of color, and typography influenced their impression of site credibility. Ivory and Hearst (2002) report that visual parameters like font size, colors used, and persistent navigation contribute to the quality ratings of a Web site. Ozok and Salvendy (2000; 2004) find that users commit fewer errors when the visual and linguistic attributes of information sites are consistent.
The value of consistency isn't hard to see: Sites that are consistent are easier to learn. There is positive transfer from one area of the site to the others. To ensure this, interface design guidelines tend to preach consistency. The guidelines stress that the consistency of the visual presentation is a key to usability. Shneidermann's first Golden Rule for interface design is "Strive for consistency."
Since no one had an evidence-driven definition for consistency, designers tend to interpret this recommendation quite literally. Usability experts focus sharply on continuity within an interface as a determiner of usability. But are we too focused?
When asked to review sites, usability experts tend to identify more inconsistency problems than users do. (Jeffries, Miller, Warton and Uyeda, 1991). Further, the experts often disagree about which inconsistencies are problems and how severely the problems will affect ease-of-use. (For more details about the inconsistency amongst usability experts, see Molich in last month's newsletter.)
So how much consistency is enough? And which consistencies are the important ones? And what type of evidence could we use to capture key aspects of perceived consistency?
Van der Geest and Loorbach (2005) report a study that seeks to explore users' perceptions of internal consistency on Web sites. The internal consistency of an interface reflects the similarity among the features and graphics within an interface. They accomplish this exploration through a novel application of the card sorting technique.
In card sorting, representative users are given a stack of index cards each containing one word or phrase. The words/phrases represent the information or services provided on the Web pages. Participants are asked to sort the cards into natural sets of what "belongs" together. They then order the cards within each set by interest. Finally, participants generate a category label for each set. Typically, card sorting provides results that provide the basis for the information architecture.
To explore the visual cues supporting perceived consistency across sites within a Web system, the researchers examined six sites within Dutch Higher Education Consortium. The sites included the main Consortium site and five sub-sites representing schools within the organization. All six sites were created based on the organizational style guide and templates. Although the sites were based on a common design standard, each school within the consortium clearly worked within the standard to create a unique and differentiated Web identity. The researchers also selected 24 typical pages from the sites.
To explore visual consistency, the card sorting technique was modified. Instead of presenting words/phrases to sort on a card, the researchers asked the participants to (among other tasks) sort, rank and label the 24 pages. (All words were "greeked" to ensure that the participants would focus on visual rather than linguistic information to sort the elements). After the sorting task was completed, participants were asked to describe the basis for their groupings and labels.
20 individuals participated in the card sorting task (Tullis and Wood, 2004).
Far and away, the most common cue for signaling that pages or elements should be grouped together was color. After color, participants looked to the grid/navigation structure to indicate belongingness. They looked to background elements and font about equally often (and third). The logo was identified as a component that created consistency only once in the study.
Van der Geest and Loorboch's report the following observations:
These findings indicate that designers need to take special caution when selecting colors for their designs. Users "see" color first. And they will attempt to derive a meaningful grouping from similarly colored elements ‚Äď whether the designer intends it to or not.
Van der Geest and Loorbach's study indicates that users do notice consistency within and across pages of a site. Users are prepared to and do notice and exploit some types of consistency within a Web system (color, navigation structure).
However, their findings also suggest that users do not take advantage of certain types of information that experts might identify as critical to usable consistency.
For example, users may fail to exploit other seemingly obvious connecting information, such as the logo.
That said, it seems critical that standards intending to promote usable consistency with local variability should promote the use of color as a cue, both to group and differentiate page elements and site sections. However, since color is so powerful, clear and appropriate guidance for use of color is critical to building an effective standard.
Fogg, B.J., Soohoo, C. and Danielsen, D. (2002). How do people evaluate a Web Site's credibility: Results from a large study. New York, NY: Consumer's Web Watch.
Ivory and Hearst, (March, 2003). Statistical Profiles of Highly-Rated Web Sites. ACM CHI 2002.
Jeffries, R., Miller, J.R., Wharton, C. and Uyeda, K.M. (1991). User interface evaluation in the real world: a comparison of techniques. Proceedings of the ACM CHI '91. New York, NY: ACM Press, pp 119-124.
Ozok, A.A., and Salvendy, G. (2000). Measuring consistency of Web page design and its effects on performance and satisfaction. Ergonomics 44, pp. 443-460.
Ozok, A.A., and Salvendy, G. (2004). Twenty guidelines for the design of Web-Based interfaces with consistent language. Computers in Human Behavior, 20, 149-161.
Tullis, T. and Wood, L. (2004). How many users are enough for a card-sorting study? Paper presented at the Usability Professionals Association Conference. Minneapolis, MN.
van der Geest, T. and Loorback, N. (2005) Testing the Visual Consistency of Web Sites. Technical Communication 52(1), 27-36.
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