Change in IBS-specific behaviors measured with a self-rating scale weekly during treatment for mediation analyses, and from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months for analysis of effect. IBS-BRQ is a self-rating scale measuring IBS-specific behavioral responses shown to be unhelpful and probably maintain IBS-symptoms. The scale consists of 26 items on a seven-point Likert scale from 1 (never) to 7 (always). The scale includes items related to avoidance behavior such as "I avoid certain social situations (e.g. restaurants) because of my IBS" and to toilet behavior such as "I spend more time on the toilet than ideally I would like". IBS-BRQ is both reliable and valid with a high degree of internal consistency for adults with IBS (Cronbach's α=.86). The scale differentiate significantly between IBS patients and healthy controls (F=221, P<.01).

Change in perceived stress measured with a self-rating scale weekly during treatment for mediation analyses, and from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months for analysis of effect. The PSS measures the degree to which situations are appraised as stressful. It is a self-report scale with 10 items on daily hassles and the current feeling of being able to handle problems that need to be addressed. It is a five-point Likert scale ranging from 0 (never) to 4 (very often). It is a widely used questionnaire to measure perceived stress and has adequate internal and test-retest reliability.

Change in pain reactivity measured with a self-report scale, pain reactivity scale (PRS), at baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months. PRS have 5 items about reactivity to and worry about pain. Three items are about emotional reactions to current pain. Two items affect frequency of worry about not being able to do things now, and in the future because of the pain. Questions are answered on a 6-point scale from 0 ("not at all") to 6 ("very much"). PRS has been reported to have satisfactory psychometric properties (Wicksell et al, 2011)

Change in pain interference measured with a self-report scale at baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months. Pain interference index (PII), have 6 items about interference on various activities because of pain. Questions are answered on a 6-point scale from 0 ("not at all") to 6 ("very much"). According to preliminary analysis, the instrument has satisfactory psychometric properties (Wicksell et al., 2011)

Change in function measured with a self-report scale at baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months. Functional disability index (FDI) have15 items on daily activities. Questions are related to specific activities such as climbing stairs, running 100 meters and to go shopping, and general activities such as eating meals and being in school all day. The scale ranges from 1 (no problem at all) to 5 (impossible). It is validated for children and adolescents with chronic abdominal pain with high internal consistency, α = .86 for boys and α = .91 for girls (Claar and Walker, 2006). FDI is the scale that is recommended in pediatric pain studies to measure the influence of pain on function (McGrath et al., 2008).

Change in visceral sensitivity from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months measured with a self-report scale that measures gastrointestinal symptom-specific anxiety. VSI is a 15-item scale and has a scale ranging from 0 (not at all) to 5 (totally agree). The scale has demonstrated excellent reliability as well as good content, convergent, divergent and predictive validity.

Change in gastrointestinal symptoms measured weekly with a self-rating scale during treatment for mediation analyses. The GSRS-IBS have 13 items about weekly gastrointestinal symptoms like bloating, hard stool, abdominal pain etc. It is a seven-point Likert scale from 1 (no discomfort at all) to 7 (very severe discomfort). The GSRS-IBS has excellent psychometric properties with internal consistency between α = .74 (for abdominal pain) to α = .85 (for satiety).

Change in quality of life from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months measured with a self-report scale that measures quality of life in adolescents. PedsQL Generic Core scales is a 23-item scale ranging from 0 (never) to 4 (almost always). The PedsQL is shown to distinguishe between healthy children and adolescents and pediatric patients with acute or chronic health conditions and demonstrate acceptable reliability and validity.

Change in gastrointestinal symptoms from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months measured with a self-report scale that measures gastrointestinal symptoms in children and adolescents. The PedsQL Gastro is a 9-item scale ranging from 0 (never) to 4 (almost always).

Change in inner symptoms from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months measured with a self-report scale that measures inner symptoms (e.g., headache, nausea, heart racing) that often, but not necessarily, occur in the absence of identified disease, in children and adolescents. CSI-24 is a 24-item scale ranging from ranging from 0 '(not at all) to 4 (a whole lot).

Change in anxiety symptoms from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months measured with a self-report scale that measures anxiety symptoms in children and adolescents. SCAS-C is a 45 -item scale ranging from ranging from 0 (never) to 3 (always). SCAS-C has demonstrated high internal consistency, high concurrent validity with other measures of child and adolescent anxiety, and adequate test-retest reliability.

Change in healthcare utilization and productivity loss from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months measured with a self-report scale that measures healthcare utilization and productivity. The scale has been revised to fit adolescents and consists in our study of 3 items assessing school absenteeism and 6 items assessing healthcare utilization.

Change in parents healthcare utilization and productivity loss from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months measured with a self-report scale that measures healthcare utilization and productivity. TIC-P consists of 10 items.

Change in anxiety levels in parents from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months measured with a self-report scale that measures anxiety symptoms. GAD-7 is a 7-item scale ranging from 0 (not at all) to 3 (almost every day). Evidence supports reliability and validity of the GAD-7 as a measure of anxiety in the general population.

Change in depression levels in parents from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months measured with a self-report scale that measures depression. The PHQ-9 is the depression module, which scores each of the 9 DSM-IV criteria as "0" (not at all) to "3" (nearly every day). PHQ-9 is shown to be a reliable and valid measure of depression severity in adults.

Change in parents responses to their children's abdominal pain from baseline to 10 weeks, baseline to 9 months, baseline to 15 months, baseline to 27 months measured with a self-report scale assessing protectiveness, minimizing, and encouraging responses to children's pain behavior. The ARCS is a 29-item scale.