Respondents
Parents and children engaged in an ongoing randomised controlled trial (RCT) evaluating the clinical and cost effectiveness of faecal calprotectin testing in primary care were eligible to take partFor the present study, we used purposive sampling by age, sex (children and parents), parental educational level and parental country of birth. Inclusion continued until data saturation, defined as being when interviews generated no new information on the research questions. All respondents received an email with a patient information letter and provided digital informed consent, which consistent with Dutch law, was obtained either from parents (child age <12 years), parents and child (age 12–15 years) or the child only (age >15 years).