Children's Depression Inventory 2 (CDI-2). The CDI 2 is a child-report measure of physiological, behavioral, and emotional symptoms of depression. The full-length CDI 2: Self-Report (CDI 2:SR) is a 28-item assessment that yields a Total Score, two scale scores, and four subscale scores. For each item, the respondent is presented with three choices that correspond to three levels of symptomatology: 0 (absence of symptoms), 1 (mild or probable symptom), or 2 (definite symptom). Raw scores are converted to t-scores ranging from 0 to 100, with a mean of 50 and a standard deviation of 10. A decrease in the score indicates an improvement in depressive symptoms (depressive symptoms decrease over time).

Depressive symptoms were assessed using the 13-item Depression subscale of the Behavior Assessment System for Children, 3rd Edition (BASC-3). The BASC-3 Parent Rating Scale (PRS) is a tool used to evaluate problem behaviors, including internalizing, externalizing, and adaptive behaviors. Parents rate the frequency of these behaviors on a scale from 'Never' to 'Almost Always.' T-scores are used to compare responses to normative data for children of the same age and gender. Raw scores are converted to t-scores ranging from 0 to 100, with a mean of 50 and a standard deviation of 10. A decrease in the score indicates an improvement in depressive symptoms (depressive symptoms decrease over time).

Depressive symptoms were assessed using the 13-item Depression subscale of the Behavior Assessment System for Children, 3rd Edition (BASC-3). The BASC-3 Parent Rating Scale (PRS) is a tool used to evaluate problem behaviors, including internalizing, externalizing, and adaptive behaviors. Parents rate the frequency of these behaviors on a scale from 'Never' to 'Almost Always.' T-scores are used to compare responses to normative data for children of the same age and gender. Raw scores are converted to t-scores ranging from 0 to 100, with a mean of 50 and a standard deviation of 10. A decrease in the score indicates an improvement in depressive symptoms (depressive symptoms decrease over time).

The Screen for Child Anxiety Related Disorders (SCARED) is a 41-item inventory rated on a 3-point Likert scale (0 "Not true or hardly ever true" to 2 "Very true or often true") used to screen for anxiety disorders. It provides a Total score and scores across five domains: panic/somatic, separation anxiety, generalized anxiety, social anxiety, and school phobia. The total score ranges from 0 to 82, with higher scores indicating greater anxiety. A score of 25 or higher may suggest an anxiety disorder, while scores above 30 are more specific. A decrease in score reflects symptom improvement.

The Screen for Child Anxiety Related Disorders (SCARED) is a 41-item inventory rated on a 3-point Likert scale (0 "Not true or hardly ever true" to 2 "Very true or often true") used to screen for anxiety disorders. It provides a Total score and scores across five domains: panic/somatic, separation anxiety, generalized anxiety, social anxiety, and school phobia. The total score ranges from 0 to 82, with higher scores indicating greater anxiety. A score of 25 or higher may suggest an anxiety disorder, while scores above 30 are more specific. A decrease in score reflects symptom improvement.

Self-report of disease activity using the Children's Somatic Symptoms Inventory (CSSI) 7-item (GI Subscale), will be collected. The GI symptom subscale includes items on nausea, constipation, diarrhea, abdominal pain, vomiting, bloating, and food-induced discomfort. Each item asks the child to rate the frequency and intensity of symptoms over a specific period (e.g., "In the past week, how often have you felt stomachaches?"). Response options include: 0 - "Not at all"; 1 - "A little bit"; 2 - "Somewhat"; 3 - "Quite a bit"; 4 - "Very much." Scores are summed to obtain a total score for gastrointestinal symptoms. High scores, indicating frequent or intense gastrointestinal complaints, may suggest significant distress or a need for intervention. A decrease in the score reflects symptom improvement.

Self-report of disease activity using the Children's Somatic Symptoms Inventory-(CSSI) 7-item (GI Subscale) will be collected from parents and teens. The GI symptom subscale includes items on nausea, constipation, diarrhea, abdominal pain, vomiting, bloating, and food-induced discomfort. Each item asks the child to rate the frequency and intensity of symptoms over a specific period (e.g., "In the past week, how often have you felt stomachaches?"). Response options include: 0 - "Not at all"; 1 - "A little bit"; 2 - "Somewhat"; 3 - "Quite a bit"; 4 - "Very much." Scores are summed to get a total gastrointestinal score. High scores, indicating frequent or intense symptoms, may suggest significant distress or the need for intervention. A decrease in score reflects symptom improvement.

Autonomic reactivity will be measured using Heart Rate Variability (HRV) with the Inner Balance system by HeartMath. HRV will be assessed before treatment, post-treatment, and at follow-up. The mediation effect will be estimated using the difference in regression coefficients (β1 - β2). Adolescent HRV data was collected via the InnerBalance sensor during the pre-treatment (T1) and post-treatment (T2) assessments.

The RR interval represents the time between heartbeats, while the NN interval normalizes this time, accounting for noise or artifacts. HRV measures, including the standard deviation of NN intervals (SDNN) and the root mean square of successive RR interval differences (RMSSD), are calculated from these intervals. Higher values of SDNN and RMSSD are considered more adaptive.

Participants randomized to the wait-list control group will complete the same measures of lifetime stress, autonomic reactivity, depression, and anxiety. The intervention was offered to control participants after the 6-week time point, and all 2-month follow-up surveys and assessments were completed only after finishing the Biofeedback Enhanced Treatment.

Total of all reporting groups

Participants randomized to the wait-list control group will complete the same measures of lifetime stress, autonomic reactivity, depression, and anxiety. The intervention was offered to control participants after the 6-week time point, and all 2-month follow-up surveys and assessments were completed only after finishing the Biofeedback Enhanced Treatment.

Acceptability of the Biofeedback Enhanced Treatment was assessed using adolescent- and parent-reported program satisfaction ratings on the Client Satisfaction Questionnaire (CSQ-8). Adolescents and parents completed this 8-item survey on a 4-point scale, with total scores ranging from 8 to 32; higher scores indicated greater satisfaction. Each group completed the questionnaire 6 weeks after finishing the Biofeedback Enhanced Treatment. No survey was provided to participants during the waitlist phase, as no treatment was administered during the waiting period.

Satisfaction data applies only to the Biofeedback Enhanced Treatment (BET), as the control group did not receive treatment during the first 6 weeks. Satisfaction was assessed after both groups had completed their treatments, and the data were combined for analysis. These results include data from participants who completed the Biofeedback Enhanced Treatment and the satisfaction surveys 6 weeks post-treatment (BET), with data from both groups analyzed after treatment completion.

Children's Depression Inventory 2 (CDI-2) is a child-report measure of physiological, behavioral, and emotional symptoms of depression. It is a widely used tool for assessing depressive symptoms in children and adolescents. It includes 28 items, each with three possible responses that reflect different levels of severity: 0 (absence of symptoms), 1 (mild or probable symptom), or 2 (definite symptom). Raw scores are converted to t-scores ranging from 0 to 100, with a mean of 50 and a standard deviation of 10. A decrease in the score indicates an improvement in depressive symptoms (depressive symptoms decrease over time).

This analysis includes participants who completed the baseline survey.

Children's Depression Inventory 2 (CDI-2). The CDI 2 is a child-report measure of physiological, behavioral, and emotional symptoms of depression. The full-length CDI 2: Self-Report (CDI 2:SR) is a 28-item assessment that yields a Total Score, two scale scores, and four subscale scores. For each item, the respondent is presented with three choices that correspond to three levels of symptomatology: 0 (absence of symptoms), 1 (mild or probable symptom), or 2 (definite symptom). Raw scores are converted to t-scores ranging from 0 to 100, with a mean of 50 and a standard deviation of 10. A decrease in the score indicates an improvement in depressive symptoms (depressive symptoms decrease over time).

The results include data from participants in both groups after completing the Biofeedback Enhanced Treatment. No 2-month follow-up data were collected from the control group during the waiting period, as they received the intervention at 6 weeks. Data were collected 2 months after completing the treatment in each group, and these were combined for analysis, as specified in the protocol, which outlines that the changes will be summarized within groups.

Depressive symptoms were assessed using the 13-item Depression subscale of the Behavior Assessment System for Children, 3rd Edition (BASC-3). The BASC-3 Parent Rating Scale (PRS) is a tool used to evaluate problem behaviors, including internalizing, externalizing, and adaptive behaviors. Parents rate the frequency of these behaviors on a scale from 'Never' to 'Almost Always.' T-scores are used to compare responses to normative data for children of the same age and gender. Raw scores are converted to t-scores ranging from 0 to 100, with a mean of 50 and a standard deviation of 10. A decrease in the score indicates an improvement in depressive symptoms (depressive symptoms decrease over time).

Depressive symptoms were assessed using the 13-item Depression subscale of the Behavior Assessment System for Children, 3rd Edition (BASC-3). The BASC-3 Parent Rating Scale (PRS) is a tool used to evaluate problem behaviors, including internalizing, externalizing, and adaptive behaviors. Parents rate the frequency of these behaviors on a scale from 'Never' to 'Almost Always.' T-scores are used to compare responses to normative data for children of the same age and gender. Raw scores are converted to t-scores ranging from 0 to 100, with a mean of 50 and a standard deviation of 10. A decrease in the score indicates an improvement in depressive symptoms (depressive symptoms decrease over time).

The results include data from participants in both groups after completing the Biofeedback Enhanced Treatment. No 2-month follow-up data were collected from the control group during the waiting period, as they received the intervention at 6 weeks. Data were collected 2 months after completing the treatment in each group, and these were combined for analysis, as specified in the protocol, which outlines that the changes will be summarized within groups.

The Screen for Child Anxiety Related Disorders (SCARED) is a 41-item inventory rated on a 3-point Likert scale (0 "Not true or hardly ever true" to 2 "Very true or often true") used to screen for anxiety disorders. It provides a Total score and scores across five domains: panic/somatic, separation anxiety, generalized anxiety, social anxiety, and school phobia. The total score ranges from 0 to 82, with higher scores indicating greater anxiety. A score of 25 or higher may suggest an anxiety disorder, while scores above 30 are more specific. A decrease in score reflects symptom improvement.

The Screen for Child Anxiety Related Disorders (SCARED) is a 41-item inventory rated on a 3-point Likert scale (0 "Not true or hardly ever true" to 2 "Very true or often true") used to screen for anxiety disorders. It provides a Total score and scores across five domains: panic/somatic, separation anxiety, generalized anxiety, social anxiety, and school phobia. The total score ranges from 0 to 82, with higher scores indicating greater anxiety. A score of 25 or higher may suggest an anxiety disorder, while scores above 30 are more specific. A decrease in score reflects symptom improvement.

The results include data from participants in both groups after completing the Biofeedback Enhanced Treatment. No 2-month follow-up data were collected from the control group during the waiting period, as they received the intervention at 6 weeks. Data were collected 2 months after completing the treatment in each group, and these were combined for analysis, as specified in the protocol, which outlines that the changes will be summarized within groups.

Self-report of disease activity using the Children's Somatic Symptoms Inventory (CSSI) 7-item (GI Subscale), will be collected. The GI symptom subscale includes items on nausea, constipation, diarrhea, abdominal pain, vomiting, bloating, and food-induced discomfort. Each item asks the child to rate the frequency and intensity of symptoms over a specific period (e.g., "In the past week, how often have you felt stomachaches?"). Response options include: 0 - "Not at all"; 1 - "A little bit"; 2 - "Somewhat"; 3 - "Quite a bit"; 4 - "Very much." Scores are summed to obtain a total score for gastrointestinal symptoms. High scores, indicating frequent or intense gastrointestinal complaints, may suggest significant distress or a need for intervention. A decrease in the score reflects symptom improvement.

Self-report of disease activity using the Children's Somatic Symptoms Inventory-(CSSI) 7-item (GI Subscale) will be collected from parents and teens. The GI symptom subscale includes items on nausea, constipation, diarrhea, abdominal pain, vomiting, bloating, and food-induced discomfort. Each item asks the child to rate the frequency and intensity of symptoms over a specific period (e.g., "In the past week, how often have you felt stomachaches?"). Response options include: 0 - "Not at all"; 1 - "A little bit"; 2 - "Somewhat"; 3 - "Quite a bit"; 4 - "Very much." Scores are summed to get a total gastrointestinal score. High scores, indicating frequent or intense symptoms, may suggest significant distress or the need for intervention. A decrease in score reflects symptom improvement.

The results include data from participants in both groups after completing the Biofeedback Enhanced Treatment. No 2-month follow-up data were collected from the control group during the waiting period, as they received the intervention at 6 weeks. Data were collected 2 months after completing the treatment in each group, and these were combined for analysis, as specified in the protocol, which outlines that the changes will be summarized within groups.

Autonomic reactivity will be measured using Heart Rate Variability (HRV) with the Inner Balance system by HeartMath. HRV will be assessed before treatment, post-treatment, and at follow-up. The mediation effect will be estimated using the difference in regression coefficients (β1 - β2). Adolescent HRV data was collected via the InnerBalance sensor during the pre-treatment (T1) and post-treatment (T2) assessments.

The RR interval represents the time between heartbeats, while the NN interval normalizes this time, accounting for noise or artifacts. HRV measures, including the standard deviation of NN intervals (SDNN) and the root mean square of successive RR interval differences (RMSSD), are calculated from these intervals. Higher values of SDNN and RMSSD are considered more adaptive.

Participants randomized to the wait-list control group will complete the same measures of lifetime stress, autonomic reactivity, depression, anxiety. The identical treatment will be offered to control participants after the 6-week time point.