Agile Development of a Digital Exposure Treatment for Youth With Chronic Musculoskeletal Pain

Participant-rated acceptability measured on 5-point Likert scale. Range 0-4 (higher scores indicate more acceptable). Questionnaire will be administered to youth with chronic pain and their parents.

Treatment satisfaction at the end of treatment will be evaluated by examining mean satisfaction scores on an adapted version of the Pain Service Satisfaction Test (PSST, McCracken et al., 1997). The PSST consists of 23 items rated on a 5-point Likert Scale (0 = not at all satisfied to 4 = very satisfied) and assesses the patient and parent's experience of the intervention. Scores range from 0-92. A score greater than/equal to 40 of 60 (satisfied to very satisfied) will indicate high levels of satisfaction with the intervention content. Caregivers were not assessed for this Outcome Measure.

As a measure of treatment adherence, we will calculate the percentage of participants who drop out or withdraw from the intervention prior to completion of the intervention.

To assess expectations for treatment effectiveness, participants completed the Credibility/Effectiveness Questionnaire (CEQ; Borkovec & Nau, 1972) after engaging with iGET Living for one week. The CEQ consists of six items rated on a 0 (not at all) to 10 (very much) Likert scale and assesses expectations related to the effects of the intervention across two subscales: Credibility (e.g., "How confident would you be recommending iGET Living to a friend with the same problems?") and Expectancy (e.g., "By the end of iGET Living, how much do you think your functioning will improve?"). Credibility is calculated by summing items 1-3 and Expectancy by summing items 4-6. Possible range of scores for each subscale is 0-30, with higher scores reflecting greater perceived credibility and expectancy.

Functional disability will be assessed using the Functional Disability Inventory (FDI, Walker & Greene, 1991), a 15-item self-report measure of perceived difficulty in performing activities in school, home, physical, and social contexts. Items are rated on a 5-point Likert scale ranging from 0 (no trouble) to 4 (impossible). Scores from all the Items are summed to create a total score (range 0-60), with higher scores indicating greater disability.

Fear of Pain Questionnaire, Child Report, Short Form (FOPQ-C-SF, Heathcote et al., 2020) is a 10-item self-report measure that assesses pain-related fear and avoidance of activities. Items are rated on a 5-point Likert scale ranging from 0 (strongly disagree) to 4 (strongly agree). Scores from all the Items are summed to create a total score ranging from 0 - 40. Higher scores indicate higher levels of pain-related fear and avoidance (worst outcome).

The Parent Fear of Pain Questionnaire (PFOPQ, Simons et al., 2015) assesses parent's fear associated with their child's pain experiences. The PFOPQ contains 23 items assessed on a 5-point Likert scale (0 = "strongly disagree" to 4 "strongly agree"). Items are summed to create a total score (0-92), with higher scores indicated greater parent fear associated with their child's pain.

The Pain Catastrophizing Scale -Child Version (PCS-C, Crombez et al., 2003) assesses negative cognitions associated with pain. The PCS-C is comprised of 13-items rated on a 5-point Likert scale (0= "not at all true" to 4 "very true"). A total score (0-52) is obtained by summing all items. Higher scores indicate higher levels of catastrophic thinking.

Pain Catastrophizing Scale-Parent Version (PCS-P, Goubert et al., 2006) assesses parents' negative cognitions associated with their child's pain. It is comprised of 13 items rated on a 5-point Likert scale (0 = "not true at all" to 4 = "very true"). A total score (0-52) is derived by summing items, with higher scores indicating higher levels of catastrophic thinking.

Child report on the Chronic Pain Acceptance Questionnaire for Adolescents-short form (CPAQ-A8, Gauntlett-Gilbert et al., 2018) will be used to assess pain acceptance in the child. The CPAQ-A8 is an 8-item measure consisting of two subscales: Activity Engagement (4 items) and Pain Willingness (4 items). Items are rated on a 5-point Likert scale ranging from 0 (Never True) to 4 (Always True) and yield a total score for each subscale ranging from 0-16. Higher scores indicate greater Activity Engagement and greater Pain Willingness (positive outcome) .

The Parent Psychological Flexibility Questionnaire (PPFQ-10, Timmers et al., 2019) is a 10-item parent self-report questionnaire assessing a parent's ability to accept their own distress and respond adaptively and flexibly to their child's pain. Items are rated on a 5-point Likert scale (0= " never true" to 4 = "always true") and are summed to create a total score, ranging from 0 - 40. Higher scores indicate greater parent psychological flexibility (positive outcome).

Adult Responses to Children's Symptoms (ARCS, Claar et al., 2010) assesses parents' behavioral responses to children's pain behaviors. The Protect subscale (13 items) will be utilized in this study. The Protect scale refers to protective parental behavior, such as giving the child special attention and limiting the child's normal activities and responsibilities. All items are rated on a 5-point Likert scale (0 = "never" to 4 "always"), and are averaged to create a total score ranging from 0-4. Higher scores indicating greater use of protective behavioral responses to their child's pain (worst outcome).