Key secondary outcome measures

See Table ​Table11 for an overview of all measurement instruments and timepoints for adolescents, parents/caregivers, and therapists.

Overview of instruments per assessment

^a T0: baseline, T1: 3 months after baseline, T2: 6 months after baseline, T3: 12 months after baseline

^b Will only be assessed in the E-TRAIN (experimental) group

Depressive symptoms as a separate construct will be measured with the Children’s Depression Inventory (CDI-2; Dutch version) [69]. The 28-item CDI-2 is a revision of the CDI [70] that assesses affective, cognitive, and somatic symptoms of depression in youth (7 to 17 years) over the past two weeks [69]. All 28 items are rated on a 3-point Likert scale from 0 to 2, and scores range from 0 to 56. The CDI-2 shows good psychometric properties [71, 72], and has been validated in adolescents up to the age of 21 [69]. To obtain a multi-informant assessment of adolescents’ depressive symptoms, the parent version of the CDI-2 will be used to asses depressive symptoms according to the parent (CDI-P) [70]. The CDI-P comprises of 17 items rated on a 4-point Likert scale, and shows good psychometric qualities [72].

Anxiety symptoms as a separate construct will be assessed with the Dutch translation of the 69-item Screen for Child Anxiety Related Disorders (SCARED; Dutch version) [73, 74]. The SCARED-NL assesses anxiety disorders according to the DSM-IV in children aged 7 to 19 years [73]. All items are rated on a 3-point Likert scale. The SCARED has demonstrated a high internal consistency, good test–retest reliability, and adequate construct and predictive validity [74, 75]. Additionally, the SCARED – Parent Version will be used to assess anxiety symptoms according to the parent (SCARED-P) [74]. The SCARED-P consists of 69 items rated on a 3-point Likert scale, and shows good psychometrics [74].

he presence of a current diagnosis of depression and/or anxiety at T2 will be assessed with the MINI (KID) (version 7.02) [55, 56]. The MINI is a structured, clinician-administered diagnostic interview that is widely used to assess the presence of psychiatric disorders based on the Diagnostic and Statistical Manual of Mental Disorders (Fifth edition; DSM-5) and the International Classification of Diseases (Tenth revision; ICD-10). For adolescents aged 13–17, sections A, B, D, E, F, G, H, U of the MINI KID will be administered. For adolescents aged 18 or 19 years, sections A, AY, B, E, D, F, FA, and N of the MINI will be administered. Both the MINI and MINI KID are well-validated, reliable interviews [54, 55, 76].

Emotion regulation will be measured with two questionnaires: the Dutch translation of Der Fragebogen zur Erhebung der Emotionsregulation bei Kindern und Jugendlichen (FEEL-KJ: Duth version) [77, 78] and the Difficulties in Emotion Regulation Scale (DERS) [79]. The FEEL-KJ is a 90-item questionnaire that assesses 15 emotion regulation strategies (i.e., problem solving, distraction, forgetting, acceptance, humor enhancement, cognitive problem solving, revaluation, giving up, withdrawal, rumination, self-devaluation, aggressive actions, social support, expression, and emotional control) in response to anger, anxiety, and sadness in children and adolescents aged 10–19 years. All items are rated on a five-point Likert scale ranging from never to almost always. The primary emotion regulation strategies are divided into two secondary scales: the adaptive and maladaptive emotion regulation scale. Total scores on the secondary FEEL-KJ scales (adaptive and maladaptive scale) will be used. The FEEL-KJ is a reliable and valid instrument to measure emotion regulation in youth [77, 80].

The 36-item DERS assesses emotion regulation difficulties across six dimensions: non-acceptance of emotional responses, difficulty in engaging in goal-directed behavior, difficulty in controlling impulses, lack of emotional awareness, limited access to emotion regulation strategies, and lack of emotional clarity [79]. For each item, respondents rate how often they engage in different behaviors or have certain feelings on a 5-point Likert scale. Total DERS scores will be used, with higher DERS scores reflecting more emotion regulation difficulties [79]. The DERS was originally developed for adults, but has demonstrated high reliability and adequate validity for adolescents [81, 82] and is widely used in adolescent-research (e.g., [25]).

To asses global functioning of the adolescents, the CBT-therapist of the adolescent will fill in the Children’s Global Assessment Scale (CGAS) [83]. Adolescents are rated on a scale from 1 (extremely impaired) to 100 (superior functioning). To measure symptom severity and improvement the Clinical Global Impression Scales will be used (CGI) [84]. The CGI-Severity (CGI-S) is a 7-item scale ranging from a score of 1 (not ill) to 7 (requires inpatient care). The CGI-Improvement (CGI-I) is a 7-item scale that compares ratings of severity with previous measures, with scores ranging from 1 (very much improved) to 7 (very much worse). Both the CGAS and the CGI are widely used measures [83, 85].