Data collection
During the annual visits, various study procedures will be conducted. Each centre in which the study visits take place (the “measurement centres”) has a dedicated team consisting of one or two research nurses, and one or two p that execute all study-related procedures. All study personnel will be trained in the study requirements and study procedures. Standard Operating Procedures (SOPs) will be provided to all study sites to enhance data quality and reduce variability in measurements as much as possible.Parents will be instructed that their children should refrain from eating, brushing teeth, using inhalation medication, and moderate to severe exercise as much as possible within 60 min prior to the visit. Drinking of water is allowed prior to the tests. Prior to the annual visits, electronic questionnaires will be sent to the parents. In the RCT study group, a subset of these questionnaires will also be sent at three monthly intervals. The parameters that are measured are listed in Fig. A web-based study management system Ldot (