User quality judgements of interactive systems

Understanding the complexities of user judgements of quality is an essential prerequisite for advancing interactive system research, evaluation, and design. Human-Computer Interaction (HCI) has led the shift from a functional system-centric definition ofquality towards a usercentred view by conceptualising usability, which has established itself as the widely accepted definition of quality within HCI. With the move of computing systems from work domains into leisure space, a whole range ofaspects beyond usability, such as pleasure, fun, and the 'user experience', are recognised as important for a system's success. As the traditional view of usability as the sole predictor for overall preference is increasingly challenged, a common understanding ofhow to incorporate such quality criteria beyond usefulness and usability into HCI is yet to be formulated. Aesthetics has thereby been receiving the most prominent share of attention in initial empirical work in the emerging user experience (UX) community, culminating in the claim that 'what is beautiful is usable'. However, empirical work is scarce and results are often conflicting. This thesis is anchored in the current discussion in HCI and UX towards a deeper understanding of the complexities of user judgement of interactive systems' quality. The thesis employs a theoretically grounded empirical investigation based on five studies of user judgement ofwebsites and a mobile content service. The thesis explores the relationships of individual quality criteria and overall preference, user biases in judgement, the relative importance of evaluation criteria for overall preference, and personal and contextual influences on user judgement, towards integrating'qualities beyond usefulness and usability in an understanding ofcontextually situated user judgement of interactive systems' quality. The thesis results demonstrate that while aesthetics can be a more powerful influence for overall judgements and preferences than traditional usability, the relationships between usability, aesthetics, and other evaluation criteria are significantly more complex. The thesis advances current understanding in HCI and UX by showing that while functional and nonfunctional attributes can both contribute to overall judgement, their relative importance depends on a personal prioritisation of the individual evaluation criteria for overall preference. The thesis further shows how the relative importance of evaluation criteria does not only depend on interpersonal differences, but also how users' prioritisations change according to the task at hand. The thesis thus significantly extends the currently accepted norm and argues for understanding user quality judgements as highly personally and contextually dependent. This reinforces the well known advice to 'know your audience' and augments it to know your audience's preferences, prioritisations, and expectations.EThOS - Electronic Theses Online ServiceGBUnited Kingdo