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Chapter 10 240 we described the custom-made framework for digitalized data collection in which we used a smartphone application as a digital end-of-day symptom diary. We found that our method led to high patient and investigator compliance and an overall state-of-the art standardized data collection with excellent completeness. Diagnostic criteria As IBS is a disorder of gut-brain interaction without a clear organic cause, the diagnosis is currently based on the presence of typical symptoms. The Manning criteria, published in 1978, were the first criteria described to aid the diagnosis of IBS 1 , followed by the Rome diagnostic criteria for FGIDs. 2 Generally, the symptom-based Rome diagnostic criteria have benefited IBS research as they have provided a clear definition of criteria patients should fulfill in IBS studies. This increases the reproducibility of research findings. Nevertheless, applicability of the criteria in daily clinical practice is limited 3 , as was also shown by a study of our group. Using a survey across 11 European countries, our colleagues found that only about one third of general practitioners (GP) use the Rome diagnostic criteria to diagnose IBS in daily practice. 4 This may reflect that the diagnostic process in IBS is challenging, despite the fact that diagnostic criteria have been defined and generally accepted. Reasons for this include: 1) IBS symptoms can resemble those of other organic disorders, e.g. inflammatory bowel disease or microscopic colitis, and the criteria do not provide clear leads to differentiate between these and IBS 5 ; 2) IBS symptoms vary considerably both between and within patients; 3) underlying pathophysiological mechanisms may differ between subgroups of IBS patients 6 ; 4) precise, objective and non-invasive biomarkers are currently not available, hence, there is no simple test that can accurately diagnose the disorder 7 ; and 5) clinicians are not aware of the symptom-based diagnostic criteria or may not be confident enough to employ them. A new problem arose when in 2016 the previous Rome III criteria were updated to the more restrictive Rome IV criteria: what to do with patients who do no longer fulfill the diagnostic criteria for IBS? These patients remain to have the same symptoms and unfulfilled needs. Using end-of-day symptom diary based surrogate markers, we investigated how the change to more stringent criteria would impact IBS prevalence ( chapter 2 ). We found that 12.6% to 38.4% of Rome III-positive patients would no longer fulfill the updated Rome IV criteria for IBS, depending on definitions used. Our results were corroborated by another study, in which the investigators found that 15% did no longer fulfill the updated IBS criteria. 8 More recent population-based studies have also confirmed the decrease in IBS prevalence when using the Rome IV criteria: Van Houte et al . and Jossan et al. found prevalence rates of 5.5% in the general Belgian population and 5.1% in a Canada-UK-US population, respectively. 9,10 This is a