Table 1.

Overview over diagnostic measures and all variables of the study

Function	Measure	Instrument	Reliability/validity	T0 baseline/ diagnostics	T1	T2	T3	T4	2-week follow-up
Diagnostic	Diagnosis	Kinder-DIPS (A)	Retest-reliability for depressive disorders=0.95 (Kappa) for the predecessor version of the Kinder-Dips for DSM-IV diagnoses in children and adolescents69	X
	IQ	CFT-20-R (A) (part 1)	Cronbach’s α=0.92 for the first part in children, adolescents and adults48	X
Primary outcome	Depressive symptoms	BDI-II (A)	Cronbach’s α=0.94 in an adolescent population70; pooled estimate for internal reliability: 0.86; discriminative validity - pooled estimate for sensitivity and specificity: 0.81; based on meta-analytical data in non-clinical and clinical child and adolescent populations71	X				X
	Negative and positive affect	PANAS-C-SF (A)	Cronbach’s α=0.86 for positive affect scale and Cronbach’s α=0.82 for negative affect scale; divergent validity - correlation between positive and negative affect scales: −0.13; based on data in an adolescent population53		X	X	X	X	X
	Perceived stress	PSS-10 (A)	Cronbach’s α=0.84; construct validity of.59 with the PHQ-2 (Patient Health Questionnaire72); based on a sample of adolescents and adults for the original version of the PSS-1073		X	X	X	X	X
	Rumination	RSQ-D (A)	Cronbach’s α=0.77 for self-focused rumination scale and Cronbach’s α=0.88 for symptom-focused rumination; convergent validity of 0.52 for symptom-focused rumination and 0.72 for self-focused rumination with the RSS (Rumination on Sadness Scale)74; based on depressed adult patients50	X				X	X
Secondary outcome	Affective behavioural responses to pictures	SAM Rating Scale (A) of valence	Cronbach’s α for SAM ratings of the stimuli applied in the current study will be calculated based on the present sample		X	X	X	X
	LPP (late positive potential)	(A)	n.a.		X	X	X	X
	Gaze fixations in emotional areas of interest	(A)	n.a.		X	X	X	X
Confounding variables	Social desirability	SES-17 (A)	Cronbach’s α=0.78 in a young adult population54 75	X
Mediators	State rumination during training	Questionnaire (A) applied in A Sanchez-Lopez, J Everaert, J Van Put, R De Raedt and EHW Koster56	Cronbach’s α=0.72 to 0.73; based on data in a young adult population56		X	X	X	X
	Habitual emotion regulation strategies	FEEL-KJ (A)	Cronbach’s α=0.93 for adaptive emotion regulation scale and Cronbach’s α=0.82 for maladaptive emotion regulation scale in children and adolescents61	X
	Executive function abilities (set shifting, working memory, inhibition)	TAP 2.3 (A)	Odd–even– reliability for reaction times in adolescents: 0.79 for working memory, 0.95 for flexibility, 0.91 for go/nogo for trials applied in the current study60	X
Moderators	Trait and state anxiety	STAI (A)	Cronbach’s α=0.91 for STAI-S scale and Cronbach’s α≥0.89 for STAI-T scale in adolescents/young adults63	X
	Psychopathology	CBCL 6–18R (P)	Cronbach’s α=0.93 for total behaviour problem scale based on a sample of children and adolescents64	X

Applied to A, adolescent; p, parent.

BDI-II, beck depression inventory; CBCL 6-18R, Child Behaviour Checklist for the ages 6-18; CFT-20-R (revidierte Grundintelligenztest Skala 2), culture fair intelligence test; DSM, Diagnostic and Statistical Manual of Mental Disorders; FEEL-KJ (Fragebogen zur Erhebung der Emotionsregulation bei Kindern und Jugendlichen), questionnaire for the assessment of emotion regulation in children and adolescents; Kinder-DIPS (Diagnostisches Interview bei psychischen Störungen im Kindes- und Jugendalter), diagnostic interview for psychiatric disorders for children and adolescents; n.a., not applicable; PANAS-C-SF, Negative Affect Scale and Positive Affect Scale for Children Shortened Version; PHQ, Patient Health Questionnaire; PSS-10, Perceived Stress Scale 10; RSQ-D, German Version of the Response Styles Questionnaire; SAM, self-assessment manikin rating scale; SES-17, Social Desirability Scale; STAI, State-Trait-Anxiety Inventory; TAP, (Testbatterie zur Aufmerksamkeitsprüfung) test battery of attentional performance.