Efficacy and Cost-effectiveness of Internet-delivered CBT for Adolescents With Depression

CDRS-R is a semi-structured clinician interview, assessing level of depressive symptomatology. Total range is 17-113, with higher values representing a worse outcome.

CGI-S was developed to assess how mentally ill a specific patient compared to a particular patient population (e.g. with major depressive disorder) at a certain time. It consists of a single item rated on a seven-point scale ranging from 1="no symptoms" to 7="extreme symptoms".

CGI-I is developed to assess improvement of psychiatric symptoms for a specific patient compared to baseline. It consists of a single item rated on a seven-point scale ranging from 1="very much improved" to 7="very much worse".

The CGAS is a single item 1-100 scale that integrates psychological, social, and academic functioning in children as a measure of psychiatric disturbance. Higher values represent a better outcome.

The iiPAS is a clinician-rated measure of patient adherence to internet-delivered behavioral interventions (38) with 5 items rated on a 0 to 4 Likert scale with total score ranging from 0 to 20, where 0 indicates no adherence and 20 perfect adherence. The scale covers client's work pace, engagement, communication with the therapist, motivation for change, and login frequency. The iiPAS has demonstrated excellent internal consistency and good construct validity as well as a strong association with objective measures of patient activity in ICBT(38). For participants in the self-guided group, we will use an adapted version excluding item 3 since communication with therapist is not applicable, and a research assistant will make the rating at post-treatment.

The ASA is an adolescent specific measure of anhedonia with 14 items with a four graded-scale from 0 (never) to 3 (always), ranging from 0 to 42 points. A higher score indicates more anhedonia. The ASA has high test-retest reliability and good convergent validity with standardized measures of depression.

The ARI is a measure of irritability, consisting of six items with a three graded scale and one item on impairment due to irritability, ranging from 0 to 12 points with higher scores indicating a worse outcome. The ARI has demonstrated an excellent internal consistency and differentiates cases from controls in a clinic a community sample.

The BADS-S is designed to track changes in proposed mediators of behavioral activation, e.g. activation and avoidance. Total range is from 0-54 with higher values indicating higher degree of activation and lower degree of avoidance. Changes during treatment in proposed mediators of behavioral activation on the BADS-S will be reported for the ICBT interventions.

To assess if the adolescent has received other psychological treatments during the trial period, the adolescents answer questions about other potential psychological treatments they have received apart from the interventions included in the trial.

The CSQ-8 is an 8-item self-rated 4-point scale, measuring different aspects of satisfaction with treatment, e.g. perception of quality of treatment, if the treatment adequately addressed their needs and overall satisfaction. Total range is 8 to 32, with higher values indicating higher satisfaction. Mean in total satisfaction scores on the CSQ-8 for each treatment group at end of treatment and at follow-up will be reported.

ISI, a brief screening measure of insomnia, a seven-item scale ranging from 0 to 28 points, with higher values representing a worse outcome.

Kidscreen-10 assess the adolescents' general health-related quality of life. Total range from 10-50, with higher values indicating better health-related quality of life.

Investigate whether the participant considers her/himself in need of further treatment for her/his depression. The scale ranges from 0 (no need for more treatment) to 4 (great need for more treatment) where higher scores indicate a worse outcome.

NEQ-20 investigates participants' negative effects of psychological treatments. Total range is 0-80, with higher values representing a worse outcome.

The RCADS-S, a shortened version of the Spence Child Anxiety Scale, is a child and parent self-report measure of anxiety- and depression-related psychopathology. Only the anxiety subscales are administered in this study since depressive symptoms are measured thoroughly by other measures. Total range is 0-45, with higher values representing a worse outcome.

The QIDS-17 covers the nine symptoms defined in the Diagnostic Statistical Manual of Mental Disorders (DSM-5) of depression rated in a scale from 0 (none) to 3 (highest) with a sum-range of 0-27. A total score of 6-10 indicates mild depression, 11-15 moderate, 16-20 severe and 21 and above very severe. Response is defined as a reduction by half of the initial score on QIDS-17. Remission is defined as below 6 points on QIDS-17. The QIDS-17 is a very reliable measure and most discriminating at moderate levels of depression.

WSAS-Y is a parent- and adolescent-rated scale of impaired functioning in school, everyday life, friends and social life, recreation and hobbies and family and close relationships. The scale generates a global score ranging from 0 to 40, with higher scores indicating greater impairment.

The EEAC is a validated self-rated questionnaire of the caregiver's positive and negative emotions directed towards the adolescent. The EEAC include 20 adjectives (each scored 1-8 where 1 indicates never and 8 always).

The TiC-P assess healthcare and societal resource use, including for example items on healthcare resource use, medications, school absenteeism, and parental productivity loss. In the present study no health economic evaluations will be conducted. Rather this instrument is included to gain feasibility data in preparation of a planned larger randomized controlled study. Therefore, no data on TiC-P will be reported in this trial.

The TiC-P assess healthcare and societal resource use, including for example items on healthcare resource use, medications, school absenteeism, and parental productivity loss.

Four qualitative questions about treatment credibility will be administered at week 3, asking how well the treatment suits adolescents with depression, how much they believe this treatment will help him/her, if and to what extent they would recommend this treatment to a friend with depression and how much improvement they expect from the treatment. Each item is scored on a 5-point Likert scale, from 1 to 5. The scale ranges from 4 to 20 points, where a higher score indicates a better outcome.