Table 2.

Overview of questionnaire items and scoring

Domain	Topic	Questionnaire	Items	Scoring and cut-off
Quality of life	Quality of life	EuroQol 5 dimensional 5-level (EQ-5D-5L) [42]	5 items (mobility, self-care, usual activities, pain/discomfort and anxiety/depression), with a 5-point Likert scale: “no problems” to “extreme problems/unable to” The EQ-5D-5L also includes a numeric scale in which participants rate their current overall health	A health state index value will be calculated from individual health profiles using the Dutch standard reference value set [49], with values ranging from − 0.446 (worse than death) to 1 (the value of full health) The numeric scale ranges from 0 (worst health imaginable) to 100 (best health imaginable)
Physical health	Fatigue	Checklist Individual Strength (CIS)-8 [43]	8 items with a 7-point Likert scale: “no, that is not right” (1) to “yes, that is right” (7)	The total score ranges from 8 to 56, where fatigue is indicated by a score of 27 or higher. A score of 27–35 indicates mild fatigue, a score higher than 35 indicates severe fatigue [50]
	Frailty	Clinical Frailty Scale (CFS) [44]	One-item scale on which a score of 1 indicates a very fit person, and a score of 9 indicates a terminally ill person	A score between 5 and 9 will be considered “frail” and a score between 1 and 4 will be considered “non-frail” [51]
	New physical problems	New physical problems after ICU admission [45]	30 items (i.e., pain, muscle weakness, loss of taste, shortness of breath) with a 4-point Likert scale: no problems, mild, moderate or severe problems	Answers will be dichotomized into “no problems” (no or mild problems) or “problems” (moderate or severe problems)
Mental health	Anxiety and depression symptoms	Anxiety and depression subscales of the Hospital Anxiety and Depression Scale (HADS) [46]	Both subscales consist of 7 items with a 4-point Likert scale ranging from 0 to 3	Each subscale has a total score ranging from 0 to 21. A score of 8 or higher on the anxiety or depression subscale indicates symptoms of anxiety or depression, respectively. A score of 8–10 indicates mild symptoms, 11–14 moderate symptoms, and 15–21 severe symptoms
	Post-traumatic stress disorder (PTSD) symptoms	Impact of Event Scale (IES)-6 [47]	6 items with a 5-point Likert scale: “not at all” (0) to “extremely” (4)	Total score is the mean of the six items, ranging from 0 to 4. A mean score of 1.75 or higher on all questions will be used as a cut-off score to differentiate between presence of PTSD symptoms or not [52]
Cognitive health	Cognitive impairment	Cognitive Failure Questionnaire (CFQ)-14 [48]	14 items with a 5-point Likert scale: “never” (0) to “very often” (4)	The total score ranges from 0 to 56. After transformation of the scores to a 0–100 range, cognitive impairment is indicated by a score of 43 or higher [53]