RAND 36. Health-related quality of life was measured with the RAND 36 (which is identical to the 36-item short form health survey [SF36]). This questionnaire contains 36 questions that record several dimensions of general well-being during the previous 4 weeks. The items are formulated as statements or questions with Likert scale response options. The 36 questions are organized into eight scales (physical functioning, physical pro-blems, bodily pain, general health, vitality, social functioning, emotional problems, and mental health) that are linearly converted to a scale of 0 to 100. The first three para-meters measure physical health, the last three parameters measure mental health, and the general health and vitality scales are sensitive to both physical and mental health outcomes. Higher scores represent better quality of life18. Normative data by age are available for the Dutch population19.
Multidimensional Fatigue Inventory-20. The Multidimensional Fatigue Inventory-20 (MFI-20) records fatigue and contains 20 statements, organized into five scales (general fatigue, physical fatigue, reduced activity, reduced motivation, and mental fatigue), with a maximum score of 20 on each subscale20. Higher scores indicate a higher level of fatigue or impairment. Dutch normative data were derived from Smets et al.21.
Hospital Anxiety and Depression Scale. The Hospital Anxiety and Depression Scale (HADS) consists of 14 items pertaining to anxiety and depression22. Each item is scored as a number, with a maximal score for each subscale (anxiety or depression) of 21. Higher scores indicate more severe anxiety or depression. A score of 6 or higher on the depression scale or 7 or higher on the anxiety scale indicates clinical depression or anxiety. Dutch normative data were derived from Spinhoven et al.23.
Cognitive Failures Questionnaire. The Cognitive failures Questionnaire is a measure of everyday cognitive problems. This 25-item questionnaire measures failures in perception, memory, and action in everyday life. The total score ranges 0-100, with higher scores reflecting more cognitive problems24,25.