visitors. This is why several early user experience publications focus on website user experience. The field of user experience represents an expansion and extension of the field of usability, to include the holistic perspective of how a person feels about using a system. The focus is on pleasure and value as well as on performance. The exact definition, framework, and elements of user experience are still evolving. User experience of an interactive product or a website is usually measured by a number of methods, including questionnaires, focus groups, observed usability tests, user journey mapping and other methods. A freely available questionnaire (available in several languages) is the User Experience Questionnaire (UEQ). The development and validation of this questionnaire is described in a computer science essay published in 2008. Higher levels of user experience have been linked to increased effectiveness of digital health interventions targeting improvements in physical activity, nutrition, mental health and smoking. Google Ngram Viewer shows wide use of the term starting in the 1930s. "He suggested that more follow-up in the field would be welcomed by the user, and would be a means of incorporating the results of user's experience into the design of new machines." Use of the term in relation to computer software also pre-dates Norman. Influences on user experience Many factors can influence a user's experience with a system. To address the variety, factors influencing user experience have been classified into three main categories: user's state and previous experience, system properties, and the usage context (situation). Understanding representative users, working environments, interactions and emotional reactions help in designing the system during User experience design. Momentary emotion or overall user experience Single experiences influence the overall user experience: the experience of a key click affects the experience of typing a text message, the experience of typing a message affects the experience of text messaging, and the experience of text messaging affects the overall user experience with the phone. The overall user experience is not simply a sum of smaller interaction experiences, because some experiences are more salient than others. Overall user experience is also influenced by factors outside the actual interaction episode: brand, pricing, friends' opinions, reports in media, etc. One branch in user experience research focuses on emotions. This includes momentary experiences during interaction: designing affective interaction and evaluating emotions. Another branch is interested in understanding the long-term relation between user experience and product appreciation.