Hoe meet je de kwaliteit van leven van kinderen met een chronische ziekte?

The development of a new disease-specific instrument to measure Quality of Life (QoL) asks for a specific methodology. This paper uses the development of a QoL instrument for children with inflammatory bowel disease as an example to illustrate this methodology. In the first phase of item generation, all potentially relevant items are gathered, using patients, experts in the field, and the literature. This phase is crucial for the development of a questionnaire that truly measures the QoL as patients perceive it. In the next phase, that of item reduction, this redundant list is reduced to including only the most relevant items to the patient population. In the instrument-formatting phase, the final number of items is chosen, the domain structure set and question and answering formats applied. In a pilot study, clearness and readability of the instrument are tested. In the validation phase, feasibility, reliability, and validity are tested. A disease-specific questionnaire is best capable of detecting small differences in QoL. This is however only possible with an instrument that is developed in a thorough way. This paper gives insight into the methodology of developing a disease-specific QoL instrument.