How consistent is your web design?

Previous studies have indicated that when interfaces are designed consistently with regards to structure and physical attributes, higher performance and lower error rates are achieved than when interfaces are designed inconsistently. The objective of the current study was to develop a methodology to measure all aspects of computer interface consistency and assess the impact of linguistic inconsistency of interface design on user performance. Based on the background literature, seven factors were identified as affecting overall consistency. Based on this identification, a structured questionnaire of 125 items was developed and a factor analysis was conducted which reduced the number of items in the questionnaire to 94 and identified the following nine factors which contribute to consistency: text structure, general text features, information representation, lexical categories, meaning, user knowledge, text content, communicational attributes and physical attributes. A series of four experiments were conducted with 140 subjects using four different tasks and eight different interface types. The internal reliability of the questionnaire was 0.81, and the inter-rater reliability was 0.75. The instrument effectively identified all of the inconsistencies in interface designs. The instrument can be utilized both as an evaluation and as a design tool for Web-based interfaces.