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Chapter 10 244 The importance of appropriate measurement tools Use of inappropriate symptom measurement tools is another factor that may impede clinical trial design, the measurement of treatment response, and therefore the development of novel (cost-effective) therapies. In the PERSUADE study, we used a custom-made smartphone application as a digital symptom diary, web-based patient questionnaires, and an electronic case report file, collectively resulting in standardized data collection with high patient and investigator compliance ( chapter 9 ). Compared to traditional paper diaries and questionnaires, this digital approach has led to a reduction in recall- and ecological bias, shows a higher adherence and provides more real time data, contributing to the methodological soundness of our RCT. Optimal symptom measurement tools may diminish biased trial results and enable clinicians and policy makers to draw more valid conclusions about treatment efficacy. Another example of a more real time registration of IBS symptoms, is the Experience Sampling Method (ESM). Akin to the digital end-of-day symptom diary used in the PERSUADE trial, the ESM is an electronic questioning method. In contrast to end-of-day symptom questionnaires, the ESM applies random and repeated measurements in the subject’s natural environment for several consecutive days. Our research group is in the process of validating an ESM patient reported outcome measure (PROM) specifically for IBS and this will help to gain further insight into fluctuations in IBS symptoms and potential triggers. 28 This more detailed insight will further enable a more personalized medicine approach (that may also be more cost-effective). In addition, validated multi-item ESM- PROMs developed according to FDA guidelines can also be used in clinical trials to evaluate treatment response. Future studies should assess whether this would alter findings of efficacy endpoints, and if yes – to what extent, in comparison to digital end- of-day questionnaires or Interactive Voice Response (IVR) systems. Targeted treatment with peppermint oil Regardless of whether we had selected the appropriate outcome measures in our RCT, assessed them with the most optimal measurement tool, or included the correct target population, we had anticipated greater treatment efficacy of peppermint oil in patients with IBS. In contrast to the highly favorable number needed to treat of 2-3 that had been found in prior (less well designed) studies, we showed a number needed to treat of 8. Advantages of small-intestinal release peppermint oil as an initial treatment compared to other pharmacological options for IBS are its availability as a low-cost over the counter (OTC) drug and the general mild and transient adverse event profile without the risk of