Table 1 Constructs and measures

 Treatment barriers

Barriers for Adolescents Seeking Health (BASH) [46] (adolescent) (Cronbach’s α: 0.75 in the R21 study)

BASH: baseline, post-MCI sessions, weeks 4, 8, 12

 Treatment attitudes

Child Help-Seeking Scale (HSS) [47] (adolescent) (Cronbach’s α: 0.70 in the R21 study); Attitudes Toward Psychological Help Scale (ATPHS) [48] (adolescent) (Cronbach’s α: 0.69 in the R21 study)

HSS: baseline, post-MCI sessions, weeks 4, 8, 12; ATPHS: baseline, post-MCI sessions, weeks 4, 8, 12

 Treatment motivation

Stages of Change (SOC) [49,50,51] (adolescent) (Cronbach’s α: 0.75–0.87 in the R21 study)

SOC: baseline, post-MCI sessions, weeks 4, 8, 12

 Alliance

Penn Helping Alliance (Haq-R) [52] (Adolescent) (Cronbach’s α: 0.89 in the R21 study)

Haq-R: post-MCI sessions, weeks 4, 8, 12

 Treatment integrity

MCI Integrity Scale (therapist)

Completed after each session

 Perceived relevance of treatment

Barriers to Treatment Participation Scale (BTPS) [53] (caregiver) (Cronbach’s α: 0.86)

BTPS: baseline, post-MCI sessions, weeks 4, 8, 12

 Caregiver knowledge about depression

Understanding Mood Disorders Questionnaire (UMDQ) [54] (caregiver) (Cronbach’s α: 0.84–0.90)

UMDQ: baseline, post-MCI sessions, weeks 4, 8, 12

 Caregiver knowledge about MH services

Therapy Survey (TS) [55] (caregiver) (Cronbach’s α: 0.52)

TS: baseline, post-MCI sessions, weeks 4, 8, 12

 Social connectedness and social competence

Interpersonal Needs Questionnaire (INQ-15) [56] (adolescent) (Cronbach’s α: 0.75–0.90)

INQ-15: baseline, post-MCI sessions, weeks 4, 8, 12

 Alexithymia

Toronto Alexithymia Scale--Externally-Oriented Thinking Subscale [57] (adolescent)

TAS-subscale: baseline, post-MCI sessions, weeks 4, 8, 12

 Empathy

Empathy Questionnaire for Children and Adolescents [58] (adolescents)

EmQue-CA: baseline, post-MCI sessions, weeks 4, 8, 12

 Adolescent engagement

Progress of Treatment (POT) [59] (therapist)

POT: after each session (MCI+IPT-A)

 Caregiver engagement

Engagement Measure (EM) [60] (caregiver, therapist) (Cronbach’s α: 0.98)

EM: weeks 4, 8, 12

 Therapist engagement

Evidence-Based Practice Attitude Scale (EBPAS) [61] (therapist) (Cronbach’s α: 0.77)

EBPAS: pre-MCI session, post-MCI sessions, weeks 4, 8, 12

 Depressive symptoms

Hamilton Rating Scale for Depression (HRSD) [62] (independent evaluator or research staff); Center for Epidemiologic Studies Depression Scale for Children (CES-DC) [63] (adolescent)

HRSD: screen, baseline, post-MCI session, weeks 4, 8, 12; CES-DC: screen, baseline, weeks 4, 8, 12

 Suicide ideation

Suicide Ideation Questionnaire-Junior (SIQ-JR) [64]; Columbia-Suicide Severity Rating Scale (C-SSRS) [65]

SIQ-JR: baseline, weeks 4, 8, 12; C-SSRS: baseline, weeks 4, 8, 12

 Global functioning

Global Functioning Scale for Children (C-GAS) [66] (independent evaluator or research staff); Clinical Global Improvement (CGI) [67] (independent evaluator or research staff)

C-GAS: baseline, weeks 4, 8, 12; CGI: baseline, weeks 4, 8, 12

 Demographics

Demographic Form (DF) (caregiver)

DF: baseline