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Smart Data Collection for the Assessment of Treatment Effects in IBS 215 9 of the questionnaires is given in the Supplementary Material. Primary efficacy results of the PERSUADE study have been described elsewhere. 16 Digital symptom diary: smartphone application For the digital symptom diary, an electronic smartphone application was developed by the center for data and information management at Maastricht University (MEMIC), in close collaboration with the investigators. The app was programmed using Xamarin, a framework to develop cross-platform applications by using programming language C sharp (C#). The PERSUADE app supports Android and iOS devices. A Maastricht University industrial designer designed the visual content. A MEMIC team of data- managers and researchers of the MUMC+ Neurogastroenterology group tested the application and provided feedback throughout several phases of development. Additionally, a patient was asked to use the diary and provide feedback regarding its user-friendliness. Patient inclusion could commence once a version was reached that all agreed on. The application’s home screen consisted of three main elements, the daily end-of-day symptom questionnaire, a medication list, and the Bristol stool chart questionnaire ( Figure 9.1 ). The end-of-day symptom questionnaire included one main question to assess the primary outcome (in accordance with FDA guidelines): “How would you rate your abdominal pain today? Think about the worst abdominal pain today” (0=no pain, 10=worst possible pain) ( Figure 9.2 ). The daily symptom questionnaire was accessible between 6 and 12pm and was unavailable outside this time window, to avoid premature completion. Other daily questions were related to ‘need of rescue medication’, and ‘adverse events experienced’. If a patient had not completed the daily entry before 10 pm of that particular day, one push notification was given. At the end of each week, the end-of-day questionnaire consisted of additional questions regarding abdominal discomfort, abdominal bloating, abdominal cramping, belching, nausea, and urgency during the last week (on an 11-point NRS, 0=no symptoms, 10=worst possible symptoms). There was no possibility to enter data from previous days and participants could not review prior entries. Automated routing, response requirements, and real- time data verification were built in to increase data-quality and completeness. The medication list was used once to register all regular medication use. Patients were asked to keep their concomitant medication use as stable as possible. However, if alterations were needed, they were able to delete, add, or change dosage of (non GI-) drugs.