The concept of usefulness has implicitly played a pivotal role in evaluation research, but the meaning of usefulness has changed over time from system reliability to user performance and learnability/ease of use for non-experts. Despite massive technical and social changes, usability remains the "gold standard" for system evaluation. However, as user experience (UX) emerges as the dominant paradigm in HCI, it is necessary to consider whether usability is sufficient and if the meaning of usefulness needs to be updated to reflect the complexity of modern interactive computing experiences.;This dissertation describes the results of a repeated measures laboratory experiment to investigate the nature and meaning of usefulness and its relationship to common UX attributes: usability, aesthetics, and enjoyment. Quantitative and qualitative analyses showed that the usefulness of a system is shaped by the context in which it is used, that usability is a major element of usefulness, that usefulness has both pragmatic (e.g., usability, simplicity) and hedonic (e.g., aesthetics, pleasurable interactions) attributes, and that usefulness plays a pivotal role in defining users' overall evaluation of a system (i.e., its goodness).;These results have several implications for evaluators of interactive systems: first, evaluators should be trained to look beyond usability and probe for issues related to usefulness: second, the scope of evaluation should be broadened to include both pragmatic and hedonic elements: third, evaluators should vary evaluation contexts to simulate the complexity of real world interactive experiences. Future research will clarify and extend our understanding of usefulness by examining usefulness in other contexts, supplementing laboratory studies with naturalistic inquiries, and developing new evaluation methods that reflect the multi-faceted nature of usefulness.
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