The objective of the current study is to propose a tool by which to measure the consistency of interfaces on World Wide Web. This tool is reliable, portable, inexpensive to administer and sufficiently easy to use. The tool consists of thirty-two questionnaire items which (1) facilitate the design of consistent websites and, hence, increased usability and (2) help identify those attributes of consistency that matter the most. A pilot study was conducted with twenty-eight subjects. Inter-coder reliability was computed to assess reliability among evaluators. The reliability of the questionnaire items was high with a measured inter-reliability of 0.88 indicating that, as a whole, the instrument is reliable, an alpha-reliability .83 for subjects' reaction to the tool indicating that the questionnaire is easy to understand and use, and an inter-coder reliability of 0.78, indicating that subjects' responses are consistent with those of other evaluators. From the results, one can deduce that subjects answered the questions with a good understanding of the items in the questionnaire. In addition, the instrument effectively identified all of the inconsistencies in the assigned websites. The experimental findings identified color and physical layout (i.e. positions of the items) as the primary consistency attributes. Findings also identified consistency of the header, global navigation area, search and the help panel as important attributes. The main content area emerged as the least important for consistency since this area would change depending on the context or specific task.
