| Outcome | Instrument | Score calculation and interpretation |
|---|---|---|
| Pain severity | Numerical rating scale-11 (NRS-11) | Severity of pain and/or discomfort in the past week is rated on an 11-point NRS scale from 0 (no pain) to 10 (worst pain). Higher scores indicate higher pain severity |
| Pain intensity and frequency | Abdominal pain diary of 7 consecutive days | Pain intensity score: an affective facial pain scale consists of nine faces, ranging from no pain at all (score 0) to the most severe pain (score 3). The pain intensity score is the sum score of 7 days (range 0–21) Pain frequency score: pain duration is measured in categories, ranging from no pain (score 0), 1–30 min (score 1), 31–120 min (score 2), to >120 min (score 3). The pain frequency score is the sum score of 7 days (range 0–21) |
| Health-related Quality of Life (HR-QoL) | KIDSCREEN-52 questionnaire | Fifty-two items are covered in 10 HR-QoL dimensions: physical wellbeing, psychological wellbeing, moods and emotions, self-perception, autonomy, relations with parents and home life, social support and peers, school environment, social acceptance (bullying), and financial resources. Each item is rated on a five-point Likert scale. Rasch scores are computed for each dimension, and are then converted to T-value norms with a mean of 50 (standard deviation of 10). Higher T-values indicate a better HR-QoL and wellbeing |
| Pain beliefs | Pain Beliefs Questionnaire (PBQ) | A total of 32 items consists of a pain belief statement that range from not true at all (score 0) to very true (score 4). Three subscales are the sum of their items: pain threat (20 items), problem-focused coping efficacy (six items), and emotion-focused coping efficacy (six items). A higher score on the pain threat scale indicates stronger belief that their abdominal pain is a threat (range: 0–4). Higher scores on both coping subscales indicate stronger beliefs in their ability to cope with pain (range: 0–4) |
| Anxiety and depression scores | Revised Anxiety and Depression Scale-short version (RCADS-25) | This questionnaire comprises 20 items of anxiety and five items of depression disorders. Items are rated on a four-point scale from 0 (never) to 3 (always). A total score for anxiety and depression is the sum of their corresponding items. Higher scores indicate more symptoms of anxiety (range: 0–60) or depression (range: 0–15) |
| Somatisation | Children’s Somatisation Inventory (CSI) | Physical symptoms in the previous 2 weeks are rated on 35 items using a five-point Likert scale ranging from no problems (score 0) to a lot (score 4). A total score is the sum of all items, with higher scores indicating more somatic complaints (range: 0–140) |
| Sleep disturbances | Dutch Sleep Self-Report questionnaire | Three items are questioned: ‘Do you fall asleep in about 20 minutes?’ (score reversed), ‘Do you wake up at night when your parents think you are asleep?’, and ‘Do you feel sleepy during the day?’ The frequency in the past week is rated as rarely (0–1 times), sometimes (2–4 times), and usually (5–7 times). A higher frequency indicates more sleep disturbances |