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230 Chapter 11 We invited families who were eligible to participate during their follow-up visit to the pediatric gastroenterology outpatient clinic in either a tertiary hospital in Amsterdam (the Netherlands) or a secondary care center in Almere (the Netherlands). All parents signed informed consent forms and all children≥8 years of agewho filled out a questionnaire signed an assent form. All participants were informed that information from the questionnaires would not be shared with their treating physicians. This study was approved by the institutional review board of the Academic Medical Center. Questionnaire For children <8 years of age, parents were asked to complete the questionnaire (proxy- report). For children ≥8 years of age, both parents and children were asked to complete separate questionnaires (proxy-report and self-report). The contents of the children’s questionnaires were similar to the parent’s questionnaires, only with age-appropriate language. Completing the questionnaire took approximately 10 minutes and was done either directly after the outpatient clinic visit at the hospital or at home, after which questionnaires were returned via mail. In addition to questions on socio-demographics, the study questionnaire incorporated five validated questionnaires: the Medication Adherence Report Scale (MARS-5) 17 , the Beliefs about Medication Questionnaire (BMQ) 18 , the Brief Illness Perception Questionnaire (B-IPQ) 19 , the Treatment Satisfaction Questionnaire for Medication (TSQM) 20 , and the Satisfaction with Information about Medicines Scale (SIMS). 21 For a previous study, these questionnaires have been translated into Dutch and afterwards translated back to English to ensure validation of the translation. 13 Medication Adherence Report Scale (MARS-5) The MARS-5 questionnaire assesses medication adherence via five statements, scored on a 5-point Likert scale (1= always true and 5 = never true), resulting in a score ranging from 5 to 25. 17 The higher the score, the more adherent patients are considered to be. One item assesses unintentional nonadherence (“I forget to take the medication”) and four items relate to intentional nonadherence. The MARS-5 score can be interpreted as a continuous variable and as a dichotomous variable (adherent versus nonadherent), in our study we chose to use both approaches. There is no consensus on which cut-off value to use for dichotomizing the MARS-5 score, cut-off values in the literature have ranged from 20 to 25. 11,17,22–33 No studies have previously used the MARS-5 in children with FC. We chose to define adherence as a MARS-5 score of ≥23, a cut-off value which has commonly been used for dichotomization of the MARS-5 in previous studies, specifically in pediatric asthma studies. 11,17,26–30