This thesis aimed to lay the foundation for a new set of Dutch mental health instruments to measure depression and anxiety in an efficient, reliable, valid, and responsive manner. More specifically, the Dutch-Flemish PROMIS adult v1.0 item banks for Depression and Anxiety were psychometrically evaluated for computerized adaptive test (CAT) administration in the Dutch clinical and general population. CAT is a modern methodology that can be used to develop instruments that measure both efficiently and reliably as only the most appropriate questions are administered, and assessment terminates as soon as sufficient reliability is achieved. For the PROMIS CAT instruments, this was demonstrated in the thesis: measuring depression and anxiety in Dutch persons was highly efficient and reliable. Moreover, the CAT instruments were shown to measure depression and anxiety sufficiently responsive and valid as well. This even includes longitudinal validity, which has barely been studied for other Dutch mental health instruments. Overall, it was concluded that the new instruments are an improvement over available instruments. Therefore, using the PROMIS CAT instruments in clinical practice may lead to more efficient and reliable measurement that supports professionals and patients in evaluating patients' treatment.This dissertation was supported by the Foundation for benchmarking mental health care (Stichting
Benchmark GGZ; SBG) and the Quality alliance mental health (Alliantie kwaliteit in de geestelijke
gezondheidszorg; Akwa GGZ).Stress and Psychopatholog