Adolescent Depression Treatment Pathways in Primary Care - a Longitudinal Cohort Study Describing Naturalistic Flow of Treatment and Evaluating Effectiveness and Cost-effectiveness of Interpersonal Counseling Compared to Treatment as Usual
Conditions: Depressive Symptoms Mild to Moderate in Severity, Major Depressive Disorder
Sponsor: Finnish Institute for Health and Welfare

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Adolescent depression treatment pathways in Primary Care – a longitudinal Cohort Study Describing 
Naturalistic Flow of Treatment and Evaluating Effectiveness and Cost-effectiveness of Interpersonal 
Counseling Compared to Treatment as Usual  
 
Running title: Protocol: treatment of adolescent depression in primary care 
 
Linnaranta, O.1,2; Myllyniemi, A. 1,3; Salusjärvi, E. 1,2,3; Seilo, N.2,4; Kaltiala, R.5; Koskinen, T.6; Karukivi, 
M.7; Karvonen, J.8; Karri, S.1, Oksanen, J.1, Heinonen, E.1,9; Kiviruusu, O.1; Therman, S.1; Berg, P. 1,3; 
Lahti, J.11,12; Rissanen, E.6; Lammintakanen, J.6; Ranta, K.5,10,13; Marttunen, M. 1,10 
1Finnish Institute for Health and Welfare, Mental Health Team, Finland 
2Itla Children’s Foundation, Finland 
3Helsinki University, Finland 
4Tampere University, Faculty of Medicine and Health Technology 
5Tampere University, Faculty of Medicine and Health Technology, and Tampere University Hospital 
Department of Adolescent Psychiatry, Finland 
6University of Eastern Finland, Finland 
7Department of Adolescent Psychiatry, University of Turku and Turku University Hospital, Finland 
8Department of Adolescent Psychiatry, Oulu University Hospital, Oulu, Finland  
9Department of Psychology, University of Oslo, Norway 
10Adolescent Psychiatry, University of Helsinki and Helsinki University Hospital, Finland  
11Department of Psychology and Logopedics, University of Helsinki, Helsinki, Finland 
12Folkhälsan Research Center, Helsinki, Finland. 
13Tampere University, Faculty of Social Sciences, Finland. 
 

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Corresponding author:  
Outi Linnaranta, M.D., Ph.D. 
Chief physician, Finnish Institute for Health and Welfare, Finland 
 

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Abstract 
Background: Implementation of evidence-based interventions is one of the proposed responses to increased 
demand for prevention and treatment of adolescent depression. While the efficacy of interpersonal 
psychotherapy (IPT-A) as an intervention to treat depression of adolescents is well established, the 
effectiveness and cost-effectiveness of the shorter adaptation, adolescent interpersonal counseling (IPC-A) 
remains open. 
Objective: We present a protocol for a prospective evaluation of the naturalistic treatment flow of adolescents 
with sustained depression, and effectiveness and cost-effectiveness of IPC-A, as compared to treatment as 
usual or no treatment of sustained depression.  
Methods: We will collect a cohort of grade 7 to 9 adolescents (13–16-year-olds) in selected Finnish schools. 
A universal evaluation of adolescents in a 6-month follow-up will provide information on the proportion of 
adolescents a) with sustained depression over the follow-up period (Patient Health Questionnaire 9 items, 
PHQ-9-A ≥ 10 in two measurements over 6 months), b) with a self-reported need for support due to depressive 
symptoms, and c) with received therapeutic intervention. We will describe the treatment received (number of 
sessions, therapeutic content) based on reports from adolescents, caretakers, and therapists, as well as 
electronic patient records. The primary outcome measure will be the proportion of adolescents who will receive 
specialized psychiatric services by 12 months after baseline. Secondary outcome measures comparing three 
groups as defined at 6 months (IPC-A, treatment as usual (TAU), or no treatment group), will include 
proportion of adolescents who received any support by 12 months after baseline, and longitudinal changes in 
PHQ-9-A scores by 12 months. Cost-effectiveness will be evaluated using survey data at 12 months, and an 
economic evaluation using register data and information on service use 12 months before and 2 and 10 years 
after baseline.  
Results: As this is the prospective registration of a protocol, we do not yet report any results from the trial. 
Funding was confirmed in 2022. Recruitment is expected to start in March 2024 and is set to finish in May 
2025. The expected baseline results will be published in the spring 2026, the 6-month follow-up by 2027, and 
the 12-month follow-up in 2028. Duration of register follow-up will be dependent on further funding. 

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Conclusions: The study will describe need for, pathways to, and content of mental health services for 
depressed adolescents. The results can improve detection and equal access to care, and inform decision -makers 
about the best practices for prevention, including utility of the implementation of IPC-A.  
Keywords: Adolescent, depression, interpersonal counseling, prevention, treatment, effectiveness, economic 
evaluation 
Introduction 
Interpersonal psychotherapy (IPT) is a structured intervention, originally developed for adults1. IPT for 
individuals with major depressive disorder has been shown to be highly effective in reducing depressive 
symptoms and anxiety, as well as improving overall functioning2,3. The acceptance and feasibility of IPT 
through adaptations for a variety of patient groups has been good1,4. 
 
IPT has been adapted for adolescents (IPT-A) for age sensitivity. However, 12 sessions of IPT-A were not 
considered to be feasible in primary care5,6. A shorter version of IPT-A, interpersonal counseling for 
adolescents (IPC-A), is composed of 3 to 8 individual sessions1. It was developed in an effort to provide a low 
threshold intervention in primary care and school health services7. Feasibility of brief IPT7 or IPC-A when 
provided by school and primary level service professionals and healthcare professionals with minimal mental 
health training has been good in four reports: two school-based, smaller studies5,7, another study with youth 
workers 8, and one among undergraduate students9. We will conduct an evaluation of IPC-A in primary care 
after a large-scale national implementation of IPC-A in primary care in 2020-2023. This will include an 
evaluation of real-world effectiveness and economic evaluation of the IPC-A intervention. 
Goal and aims 
The overall goal of this research project is to increase knowledge about clinical utility of implementation of 
evidence-based interventions in primary care. To this end, we propose a protocol to collect a cohort of grade 
7 to 9 adolescents (age about 13 to 16 years), using convenience sampling in selected Finnish schools.  

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Aims 
1. We will describe the need for support as well as treatment and naturalistic treatment flow of 
adolescents during 6 months in a population with no previous treatment of depression 
2. In a longitudinal follow-up, we will evaluate the outcome of adolescents with depressive symptoms, 
including the outcome of those with no treatment, and the effectiveness and cost-effectiveness of IPC-
A and treatment as usual (TAU),  
3. We will evaluate predictors of the treatment flow and adolescent outcome at 12 months and 2 years 
after baseline.  
Research questions 
1. Do young people reporting depressive symptoms have equal access to IPC-A or TAU in a 6-month 
follow-up, dependent on their risk for depression and independent of their area of residence, gender, or 
other minority status? (Aim 1)   
2. Is IPC-A effective and cost-effective as compared to TAU in a 12-month follow-up? (Aim 2) 
3. Can we identify characteristics of young people or therapists which most likely predict treatment 
benefits from an IPC-A intervention after 12 months and 2 years? (Aim 3)   
Hypotheses 
1. Availability of IPC-A improves access to treatment. This could be seen as a shorter time to treatment, a 
larger proportion of or a broader diversity of adolescents with sustained depression being motivated to 
and/or receiving treatment (Aim 1, RQ1) 
2. Adolescents who receive IPC-A have a better outcome, that is, are less likely to be referred to specialized 
psychiatric services and other support and services than TAU or no treatment group in the 24-month follow-
up (Aim 2, RQ 2) 
3. Self-reported adolescent inclusion, functionality, positive mental health, and loneliness predict need for a 
future intervention and outcome, and therapists’ sense of skillfulness, satisfaction with implementation, and 
sense of difficulties is a further predictor of outcome (Aim 3, RQ3) 

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Methods 
Study design 
This is a prospective, naturalistic cohort study, where treatment is not under the control of researchers but the 
sampling is based on a convenience sampling method. Inclusion criteria: We will include all adolescents 
attending grades 7 to 9 (age 13 to 16 years) in selected schools. Exclusion criteria include psychiatric care 
within the past 12 months or receiving a psychosocial intervention (psychotherapy, IPC-A, any other therapy 
or support from the same professional for >3 meetings) during the 12 months before baseline, an inability to 
reliably understand the Finnish, Swedish, English, or Finnish plain language versions of the survey, or an 
adolescent’s or caretaker’s report on need for exclusion, such as another medical condition – including a mental 
disorder – requiring acute current treatment or support. Exclusion will be made by the researcher based on the 
survey response from the adolescent and caretaker, including confirmatory information by phone where 
necessary. 
Recruitment and eligibility 
The recruitment of adolescents will be done from four university clinic areas (Northern, Eastern, Central and 
Western Finland) to provide a representative national sample based on interest of schools. Two to three 
municipalities from each university clinic area have consented to the study. 
With the consent of the school, all grade 7 to 9 adolescents (age about 13 to 16 years) in the school will have 
a session about mental health literacy skills (how to talk with friends about mental health, how to know when 
adult support is needed). The information will be adjusted for their age. During that session, the goals of the 
study will also be described. A similar session will be held for caretakers; the session will be complemented 
by messaging all parents a link to a video recording and supplementary materials for mental wellbeing online, 
as well as providing information about the study. 
Subsequently, a research assistant (RA) will help adolescents fill in a digital survey questionnaire. Upon 
agreement with the recruiting school, this can take place either after the information session or in the classroom, 
in a context of a group discussion at a general level about the dimensions of mental health and wellbeing, and 
options for help for mental health.  

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Sample size 
To estimate the number of adolescents to be screened, in the absence of available Finnish data, we used the 
information from the Netherlands Mental Health Survey and Incidence Study (NEMESIS) for incidence10 and 
prevalence findings from NEMESIS11. Based on these findings, we roughly estimated that the incidence of 
depressive disorders would be 2%6. 
For the current study, a conservative estimate is to screen 6 000 to 9 000 young people. We estimate this, with 
a 15% prevalence and 2% incidence, approximately 50% of adolescents not having previous treatment despite 
prevalent depression at baseline to the cohort, and a 70% consent rate, to recruit a minimum of 100 consenting 
adolescents to the IPC-A group, 200 consenting adolescents to TAU-group, and 100 to the depressed/no 
treatment-group. The size of any group might be considerably larger, but we will finish recruitment once the 
minimum size of all groups has been reached. 
Measures and data collection 
Data will comprise surveys for adolescents, caretakers, and therapists, as well as register data and 
complementary information on the timing, duration, and content of psychosocial support and overall treatment 
of depression (Table 1). The respondents will receive an online link they can use to respond at their 
convenience.  

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Table 1. Study flow and timing of data sources
 
A comprehensive adolescent survey 
Adolescents will complete a survey on sociodemographic information and self-evaluation measures at baseline 
and at 3 and 6 months. Those who show sustained depression (Patient Health Questionnaire 9 items (PHQ-9-
A) sum scores ≥ 10 twice during the first 6 months after baseline) will also complete the comprehensive survey 
at 12 months. The comprehensive adolescent survey is also available as a shorter version in plain Finnish 
language. 
Outcome measures in the adolescents’ and caretakers’ surveys 
We list here the self-report questionnaires (Table 2) that will be presented to adolescents and caretakers at the 
various timepoints. The questionnaires will be presented in Finnish, Swedish, or English, as suitable. 
Table 2. A summary of the content of the adolescents’ and caretakers’  surveys 
Name of the scale 
Short 
Lengt
h 
Rating 
Time 
frame 
Describes 
The Patient Health 
Questionnaire 9 items*1 
PHQ-9-A 
9 
items 
0 to 3 
2 weeks 
Depressive 
symptoms 
The child-friendly EQ-5D 
version*1 
EQ-5D-Y 
5 
items 
+ VAS 
5 items 0 to 2; 
The EQ VAS 
The same 
day 
Quality of life 
          
        
       
        
        
                        
                      
                    
      
   
   
   
                       
                     
                    
      
 
 
 
                 
 
 
                 
 
                  
            
                           
                    
            
 
         
 
              
              
 
              
       
 
       
             
                         
                         
                  
               

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Generalized Anxiety 
Disorder Scale-7 
GAD-7 
7 
items 
0 to 3 
2 weeks 
Anxiety 
Young Person's Clinical 
Outcomes in Routine 
Evaluation-Outcome 
Measure 
YP-CORE 
10 
items 
0 to 4 
1 week 
Response to 
therapy 
Do you feel lonely?1 
 
1 item 
0 to 4 
No time 
frame 
Perceived 
loneliness 
The Warwick-Edinburg 
Mental Wellbeing Scale 
SWEMWBS 
7 
items 
0 to 4 
2 weeks 
Positive mental 
health 
Experiences of Social 
Inclusion Scale 
ESIS 
10 
items 
0 to 4 
No time 
frame 
Social inclusion 
3x10D Survey* 
3x10-D 
10 
items 
0 to 10 
No time 
frame 
Functionality 
Questions about worry as 
well as need and 
willingness for treatment*1 
 
0 to 10 
VAS 
scales 
0 to 10 VAS 
scale 
No time 
frame 
Need and 
motivation for 
psychosocial 
support 
Background 
questionnaire*1 
Sociodemographic 
information, minority status 
 
 
 
NA 
 
Alcohol and substance use, 
self-harming behavior*1 
 
 
Yes/no, open 
field 
 
 
Use of health and social 
welfare services*1 
 
 
Yes/no, open 
field 
12 months 
Information to 
classify as IPC-A, 
TAU, and no 
treatment groups 
Note. Scales marked with an asterisk (*)will be used in the caretaker’s survey as a proxy version. Scales marked with 1 will be included 
in the shorter plain language version. 
The Patient Health Questionnaire 9 items (PHQ-9) is a depression severity measure based on DSM criteria. 
The items are answered according to the frequency of symptoms (0 = not at all, 1= some days, 2 = more than 
half of the days, 3 = almost every day). A higher score is indicative of greater depressive symptomatology. 
The PHQ-9 is a unidimensional measure with good internal consistency, also in adolescents12–15. In adults, the 
optimal sum score cut-off is ≥ 1016. The PHQ-9 classifies respondents’ sum scores into depression severity as 
follows: 0–4 indicates no depressive symptoms, 5–9 mild depressive symptoms, 10–14 moderate depressive 
symptoms, 15–19 moderately-severe depressive symptoms, and 20–27 severe depressive symptoms16. One 
study of 442 youth with major depressive disorder (aged 13–17 years) proposed a cut-off of ≥ 1112. We will 
use the PHQ-9-A version according to DSM-5 criteria, including irritated mood for adolescents. 

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The child-friendly EQ-5D version (EQ-5D-Y) is based on the EQ-5D-3L, which is a widely used standardized 
generic measure of health-related quality of life (HRQoL), originally designed for adults. EQ-5D-3L has been 
used internationally in many settings, such as in clinical trials and population surveys. The EQ-5D-Y was 
introduced by the EuroQoL Group in 2009 as a more comprehensible instrument suitable for children and 
adolescents than the original17. The EQ-5D consists of five questions about mobility, looking after oneself, 
doing usual activities, having pain or discomfort, and feeling worried, sad, or unhappy. Each item has three 
response alternatives. A question about general health is evaluated on a visual analogue scale (VAS)18. 
The Generalized Anxiety Disorder Scale-7 (GAD-7) is a seven-item self-rated instrument used to assess 
symptoms of generalized anxiety. Each item asks the individual to rate the severity of his or her symptoms 
over the past two weeks. Response options are 0 = not at all, 1 = several days, 2 = more than half the 
days, 3 = almost every day. GAD-7 scores can be categorized into mild, moderate, and severe anxiety with 
sum cut-offs of 5, 10, and 15 (score range 0–21). At a cut-off point of 10 or greater, sensitivity and specificity 
exceed .8019. 
 
The Young Person's Clinical Outcomes in Routine Evaluation-Outcome Measure (YP-CORE) is a ten-item 
measure designed for use in the 11–16-year age range. It is adapted for young people from The CORE-Outcome 
Measure for adults that has both 34- (CORE-OM) and 10-item versions (CORE-10)20. The CORE-OM and 
CORE-10 were developed as screening measures for psychological distress, including items for well-being, 
psychological symptoms, functioning, and risk. YP-CORE is well accepted, and the rate of missing values is 
low. Internal consistency (α = .83–.92) and test-re-test reliability is good (r = .69), and the results of 
confirmatory factor analysis (CFA) have supported a one-factor model. The YP-CORE showed good 
concurrent validity against two widely used symptom-specific measures (r = .62–.87). The measure was 
sensitive to change, showing a larger effect size (d = 0.55) than the Beck Depression Inventory (BDI-21) and 
Beck Anxiety Inventory (BAI) (d = 0.31-0.50). The Finnish translation of YP-CORE has good psychometric 
properties21. 
Perceived loneliness is a simple measure of loneliness based on self-assessment including only one question. 
This single question has been found to have good content validity in older adults22.  

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The Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS) with both its 14- and short 7- item versions 
measures positive mental health, that is, holistic aspects of wellbeing, namely eudemonic and hedonic 
wellbeing as well as psychological functioning23. This questionnaire allows for measuring mental wellbeing 
as a partially separable concept from mental illness, and has favorable psychometric properties, especially an 
approximate normal distribution in the general population. We will use the 7-item version (the Short 
WEMWBS; SWEMWBS) that has been validated in a large Finnish dataset24, and validations in adolescents 
have proved successful25–27. Using the SWEMWBS, we will be able to calculate mental health costs and 
quality-adjusted life years (QALYs)28. 
Experiences of Social Inclusion Scale (ESIS) is a brief self-evaluation instrument to assess self-reported 
experiences of social inclusion. It consists of ten statements that map the respondent's feelings of belonging, 
the significance of what they do, and the possibilities for action. One extreme of the continuum formed by the 
answers represents the experience of non-participation/social exclusion and the other the experience of 
inclusion. The participation indicator is calculated by scoring claims: a higher score means a stronger 
experience of inclusion. The sum score is scaled to a range of 0‒100. ESIS has been developed in the Finnish 
Institute for Health and Welfare (THL) Social Inclusion Coordination Project (Sokra). The theoretical 
framework is the capability approach (CA). In the validation study of the Finnish version of ESIS in adults, 
results indicated good internal reliability and consistency (α = .89), and factor analyses suggested a one-
dimensional factor structure for the ten items of the ESIS29. 
 
Functionality (3x10D Survey). The 3x10D survey is a quality-of-life mapping metric. The instrument 
comprises ten dimensions describing the life situation. The dimensions are evaluated in relation to the present 
moment, their importance, and the future. The young person evaluates areas of life for how important they feel 
the dimensions are and how satisfied they are with their current state30. The scale is awaiting international 
validation but publications from Finnish datasets are in preparation.  
Sociodemographic information  

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The comprehensive survey will include sociodemographic information collected at baseline after informed 
consent and will include information on age, self-identified gender, sex assigned at birth, first language, other 
minority status (language, sexual orientation, ethnic, other), area of residence, and household composition. 
Biweekly short survey 
Adolescents will respond to a short online survey biweekly over a 6-month follow-up, independent of their 
mood. This short survey will include PHQ-9-A and questions on their subjective need and motivation for 
treatment of depression, as well as any received treatment of depression.  
Motivation to treatment 
Need and motivation to treatment will be asked: Are you worried about your mood (yes/no). Those worried 
about their mood will further be asked: How willing are you to have help from others to improve your mood? 
This is done with a VAS with a scale from 1 to 10. This is complemented by the Motivation for Youth’s 
Treatment Scale (MYTS)31, an intrinsic treatment motivation scale for youth. The questionnaire includes 8 
questions answered on a scale from 1 (strongly disagree) to 5 (strongly agree), where higher ratings indicate 
higher motivation. Based on the participants’ answers a total scale and two subscales: Problem Recognition 
(4 items) and Treatment readiness (4 items) are calculated. The internal consistency of all three scales was 
found to be good (α = 0.84 – 0.89) and Confirmatory Factor Analysis supported the two-factor model31. 
These findings were also replicated in another study, although caution in using the total scale is warranted 
due to low correlation between the subscales32. 
Caretaker’s survey  
One caretaker, upon acceptance and choice of the adolescent, will be sent a link to consent to and twice fill in 
a survey using a secure link (within one month from baseline and at 6 months from baseline) (Table 2). The 
caretaker survey will include sociodemographic information. The scales in the caretaker survey include proxy 
versions of the PHQ-9, EQ-5D-Y, and 3x10D questionnaires, and questions about the adolescent’s mood, need 
for treatment, and willingness for treatment. We will also ask whether they or the adolescent have sought and 
received help for the adolescent, and if yes, what kind of support they received; or if not, what kind of support 
they think would be necessary. At 6 months, where applicable, we additionally ask about benefits and adverse 
effects of treatment. 
The therapist survey 

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A single survey will be sent to the therapists providing the main psychosocial support, including therapists 
providing IPC-A and other therapists. For each adolescent, the therapist will report the duration and timing of 
therapy, content, and response, including benefits and adverse effects of the intervention. We will use the 7-
item SWEMWBS to assess their own positive mental health each time they respond to a survey concerning a 
participating adolescent23.  
 
The therapist will respond once to a longer survey that will include information on their sociodemographic 
details, professional training, and specifically, the amount and quality of the training they have had in IPC-A 
or other psychotherapy. For IPC-A therapists only, we will use the Normalization Measure Development 
questionnaire (NoMAD)33 to describe the therapist’s view on the implementation process of the IPC-A and 
their ability to use their IPC-A skills. Furthermore, for all therapists, we will use the Trainee Current Practice 
Report, a comprehensive self-report questionnaire, soliciting information on psychotherapist experiences in 
their current practice. The therapist skills survey is informed by ongoing work by Professor Erkki Heinonen34, 
and was developed to assess how therapists develop during their training in the recently initiated and ongoing 
SPRISTAD study. The questionnaire features items gauging both subjective skilfulness (10 items) and 
difficulties (12 items) in therapy work, which are used also in the present investigation. In the Finnish arm of 
the SPRISTAD study34, the data of 267 psychotherapist trainees (representing various background professions, 
therapy training programs, and universities) has yielded good reliabilities (α = .89 and .84) for the two scales, 
respectively (personal communication).  
This information will be used to correlate competence and personal characteristics with the adolescent outcome 
of IPC-A or other therapy, and to complement knowledge about the impact of training procedures and 
implementation process. 
Benefits and adverse effects due to support or treatment 
Benefits and adverse effects due to support or treatment will be estimated with open field questions for the 
adolescent (“Do you feel that attending interpersonal counseling was useful for you?” (yes/no), Do you feel 
that attending interpersonal counseling was harmful for you? (yes/no), "If yes, please describe how”. Open 
field responses will be analyzed with thematic analysis. Additional statements concerning experience about 

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treatment were formulated. This format was selected while valid and gold standard instruments for evaluation 
of adverse effects of therapy have been reported to be lacking35. The comprehensive survey at 3, 6 and 12 
months contains items for potentially adverse effects (substance use and self-harm). To complement adolescent 
view, we will ask about benefits and adverse effects in the caretaker and professional’s survey with similar 
questions. 
Adolescent follow-up after 6 months 
A comprehensive adolescent survey will be repeated at 12 months for those who show sustained depression; 
no further follow-up will be done for those who were not depressed over 6 months. 
A depressed adolescent in subjective need for treatment is an adolescent who reports a need for support or 
treatment of depression. Depressed adolescents who received treatment are those who report receiving 
treatment over 6 months, in the caretaker report at 6 months indicates treatment of the adolescent for 
depression, or where register data shows contact to social or health care services. 
 
Adolescents with sustained depression (self-reported PHQ-9-A ≥ 10 twice over 6 months, including intake) 
will be classified in three groups for further follow-up based on adolescent report  
(1) Adolescents who received prevention or treatment of depression including IPC-A during 6 
months of follow-up as reported by the adolescent or a therapist, or evident from the medical 
files (aiming at n = 100 recruited in order of identification). If IPC-A is started within six 
months of the follow-up as reported by the adolescent or a therapist in medical files, the 
adolescent will be classified into this group (1) 
(2) Adolescents who received any other treatment for depression (TAU) (aiming at n = 200).  
(3) Adolescents with sustained depression, with no treatment at baseline or during six months 
of follow-up (aiming at n = 100) 
Identifying adolescents who received psychosocial support or treatment is based on the adolescent and 
caretaker reports and will be complemented from medical records, therapist reports, and/or phone calls to 
informants. 
Description of the intensity of treatment 

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Description (dosing) of TAU and IPC-A will be based on the adolescent’s, caretaker’s and therapists’ reports. 
Where necessary, the information might be complemented from medical records, and/or phone calls to 
informants. This helps in defining the adolescents as three groups (those who received IPC-A, TAU or no 
treatment), describing the overall use of resources, and calculating intervention cost for cost-effectiveness 
analysis at 12 months. 
Effectiveness of IPC-A intervention. We do not control provision or timing of IPC-A intervention as part of 
the study. However, adolescents in the IPC-A group will, even if the treatment period continues after six 
months, complete weekly reports of PHQ-9-A as it is an integral part of treatment, and this information will 
additionally be collected for the purposes of the study. Thus, even if IPC-A would continue after 6 months 
after baseline, we will be able to evaluate the response over the IPC-A period.  
Register data 
Register data will be collected to define health and social care service use and costs. Register-based data will 
include 12 months prior study to evaluate pre-trends of service use and costs. A further prospective register-
based data collection for economic analysis will be done at 2 years, 5 years, and 10 years after baseline. 
We will use four Finnish nationwide registers provided by THL: 1) Care Register for Health Care, 2) Register 
of Primary Health Care visits, 3) Care Register for Social Welfare, and 4) Register of Child Welfare. In 
addition, we will use the Drug Prescription Register (Statistics on reimbursements for prescription medicines 
and rehabilitation) from the Social Insurance Institution of Finland (Kela). The data extracted will include use 
of emergency services and hospitalizations due to suicidality and somatic complications from self-harm as 
well as for psychiatric indications, use of inpatient and outpatient services, use of primary care, reimbursements 
for medicine expenses, provision of psychotherapy or neurocognitive rehabilitation, committed suicides, use 
of child welfare services and use of social services.  
Outcome measures comparing three groups of adolescents with sustained depression (IPC-A, TAU or no 
intervention) 
Primary outcome measure 

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• proportion of adolescents referred to specialized psychiatric services during 12 months 
after baseline 
Secondary outcome measures 
• 
proportion of adolescents with any need for psychosocial or psychiatric treatment or social services 
at 2, 5, and 10 years after baseline.  
• 
longitudinal changes in PHQ-9-A score by 12 months in each of the three groups in the repeated 
adolescent surveys  
Other outcome measures 
• 
EQ-5D 
• 
GAD-7 
• 
YP-CORE-OM 
• 
loneliness 
• 
SWEMWBS 
• 
ESIS 
• 
3x10D Survey 
• 
sociodemographic characteristics, including gender and minority status 
Complications and harmful behavior during the intervention (surveys and register data) 
• 
alcohol and substance use  
• 
self-harming behavior and suicidality  
• 
hospitalizations during a therapeutic intervention  
• 
drop-out from treatment 
All analyses will be intention-to-treat, though loss to follow-up will be minimal, due to the outcome measures 
being comprehensive national registers. Cost-effectiveness will be estimated at 12 months and economic 
evaluation will be completed at 2 years, 5 years and 10 years after baseline. 

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Statistical analysis of psychometric measures 
For descriptive purposes, we will use both parametric and non-parametric descriptive statistics. Tests for non-
parametric measures will be used for testing statistical significance of correlations and between-group 
differences (IPC-A, TAU, no treatment), with the alpha level set to .05 in each analysis separately. 
Conventional psychometric characteristics of all measures will be described and compared between self-
identified cis-male and cis-female participants. If the size of a subsample is > 20, we will additionally evaluate 
adolescent groups by gender, sexual orientation, report of ethnic and other minority status, specific groups of 
first language, or plain language.  
To evaluate the validity of each scale, we will analyze the proportion of missing responses. Since there is some 
indication about limited measurement precision among adolescents for some response options36, we will use 
item response theory (IRT) or similar methods to take into account separate probabilities for response option 
of each item. In the psychometric analysis of the individual scales, we will use confirmatory factor analysis of 
categorical items to test for psychometric properties. We will also correlate PHQ-9-A with each of the other 
scales (YP-CORE, perceived loneliness, WEMWBS, EQ-5D-Y, ESIS, and 3x10D Survey). In the longitudinal 
survey dataset (baseline, bi-weekly measurements over 3 months, comprehensive surveys at baseline, 3, 6, and 
12 months), we will estimate test-retest reliability and sensitivity to change of the scales by observing change 
in PHQ-9-A in relation to changes in other scales. 
Statistical analysis of primary and secondary outcomes 
Primary outcome: Based on information from adolescent, caretaker and therapist surveys, complementary 
information and register data, we will determine whether adolescents did or did not receive specialized 
psychiatric care by 1 year, and from registers between 1 and 2 years We will use descriptive statistics to 
characterize adolescents with IPC-A, TAU and no treatment, and of main outcome measures in each group.  
Secondary outcomes: We will use register data to determine adolescents who received any other support by 2, 
5, or 10 years, as indicated by psychosocial or psychiatric treatment, use of social services, or social or medical 
benefits (yes/no) comparing three groups (IPC-A, TAU, or no treatment group, as defined at 6 months).  
PHQ-9-A of IPC-A and TAU groups during the intervention will be compared where data is available. 

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Predictors of outcome 
We will use PHQ-9-A at baseline and mixed linear modelling for individual outcome for PHQ-9-A during 
the 6 months of follow-up and test whether the three groups (IPC-A, TAU, and no treatment) differ in 
variation of symptom severity. 
We will test whether adolescent-rated SWEMWBS, YP-CORE, perceived loneliness, EQ-5D-Y, ESIS, 
3x10D Survey and GAD-7, or membership in some subgroups of >20 adolescents (gender or sex, minority 
status, functional limitations, first language, area of residence) are predictors of subjective or parent-reported 
need for treatment, or actually receiving therapy, other TAU, or other support. 
IPC-A therapist training and subjective competence will be compared to adolescent response (PHQ-9-A). 
Analysis of pathways to care 
We will describe the proportion of adolescents who receive any support for depression, who receive IPC-A, 
and time to treatment or support (Kaplan-Meyer analysis). 
We will characterize the schools and municipalities of recruitment based on the number of therapists rained 
and providing IPC-A and other professionals providing public social and health care services to the age group 
as compared to the number of adolescents at the school or municipality. This information will be used to 
evaluate the impact of availability of IPC-A therapists on likelihood of receiving any treatment for depressive 
symptoms, time to therapy/TAU treatment, and outcome of adolescents recruited to the study (Hypothesis 1). 
This will provide the estimate of utility and added value of implementation of IPC-A. 
The bi-annual School Health Survey (SHS) is a national survey, with the last round completed in spring 2023. 
Where possible, we have included the same questions as the SHS and will thus be able to estimate how 
representative our cohort is compared to mean values in the municipality. In addition to two first items of 
PHQ-9-A, the SHS survey provides information on the proportion of adolescents reporting that they have a 
subjective need for support and that they have sought support, which will allow comparing the results in the 
current study to the general finding in the SHS. 

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Economic evaluations of IPC-A 
The overall goal of the economic evaluation of IPC-A is to estimate costs and cost-effectiveness of the IPC-A 
intervention to provide information for health and social care decision-makers. The aim is to evaluate whether 
the IPC-A is cost-effective as compared to TAU and no intervention in a 6- and 12-month follow-up from a 
societal perspective. Also, we aim to evaluate the IPC-A intervention’s effect on health and societal care 
service use and costs of adolescents with depressive symptoms in 2-, 5-, and 10-year follow-ups compared to 
TAU and no treatment. The cost-effectiveness of the IPC-A intervention will be evaluated together with the 
effectiveness study at 12 months and therefore the study design will be as described previously. We will use 
the effectiveness data and registers of health and social care services and medical purchases collected as 
described above.  
The cost-effectiveness evaluations will combine both effectiveness and costs information of the IPC-A as 
compared to TAU and no treatment. Two separate analyses will be conducted. First, we will use EQ-5D-Y-
based QALYs as the effectiveness outcome. Second, we will use PHQ-9-A scores as the effectiveness 
outcome. We will apply the limited societal cost perspective including, for instance, intervention costs with 
relevant use of both health and social care services and medicine purchases from national registers. To enable 
the use of micro-costing, we will collect the resource uses from multiple sources and use National unit costs 
for health and social care services in monetarization30. Multiple imputations37 will be performed for missing 
effectiveness outcomes and cost items if needed.  
We will use standard methods of cost-effectiveness analyses, and will, for instance, apply incremental analysis 
of the effects and costs. First, we will assess dominance of the intervention, that is, whether an intervention is 
more effective and less costly. In case without clear dominance, we will calculate incremental net health benefit 
or net monetary benefit comparing the alternatives with 95% confidence intervals38.  
Data management 
Data entry: Data will be collected using the THL in-house questionnaire engine Lomakepalvelu (questionnaire 
service). 
Data coding: All participants will receive automatically generated identifiers and additional, automatically 
generated identifiers for caretakers and professionals. All survey data will be stored using this research ID. 

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Register data including person IDs will be managed using the Findata Kapseli service. Sensitive personal 
information will be stored separately from any questionnaire data. All other data will be stored pseudonymized.   
Data storage: Data will be stored on the THL database system OLAP server, where the survey data, sample 
data, and register data will be collected for analysis. Participant identifier data will be stored separately on the 
THL research and scheduling service “Tutkimus ja ajanvarauspalvelu TAP”.  
Data confidentiality: Subjects have no access to information provided from other linked persons. Data access 
is restricted by user roles with permission of PI. 
Data monitoring committee will be comprised of the senior researchers in the team (Linnaranta, Marttunen, 
Ranta, Lammintakanen, Heinonen, Lahti, Koskinen, Karvonen, Kaltiala, Oksanen) and will monitor the 
number of participants every three months (adolescents with subsequent depression who received IPC-A, TAU 
or no treatment, caretakers and professionals) and missing data. They will make the final decision about 
finishing recruitment or changing procedures to enrich recruitment for any group to reach sufficient power to 
respond to the research questions. If necessary, these modifications will be reported to the ethics committee 
and in scientific reports. Additionally, the same committee will audit data collection procedures every 6 
months. No independent auditing committee is nominated since the treatment is not under control of 
researchers. 
Results 
We expect to start recruitment of the prospective cohort in March 2024 and will finish 12-month prospective 
sampling and data collection by the end of 2025. We expect to collect the first register data at the end of 2026. 
We expect to report psychometric properties and intercorrelations of measures in the baseline survey data in 
spring 2025, 6-month follow-up data in late 2025, and 12-month follow-up data in 2027. We expect to describe 
treatment flow by 12 months, treatment (IPC-A, TAU) effectiveness, and predictors of 12-month treatment 
outcome in late 2026 or in 2027. We expect to report economic evaluation of 12-month-data in 2027. The 
economic analyses at 2-, 5- and 10-year follow-ups will be reported as the data is ready to be collected from 
registers. All main results will be reported as peer-reviewed articles in suitable international journals. 

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Discussion 
This will be a large prospective and nationally representative cohort of up to 9000 adolescents. The overall 
goal of this project is to increase knowledge about the actual, naturalistic provision, effectiveness, and cost-
effectiveness of treatment for adolescent depression in primary care. This will inform further improvements in 
detecting adolescents who would benefit from early prevention of depression and improving equal access to 
treatment of depression. 
Ethics approval 
The protocol was approved by Helsinki University Hospital Ethics board (#HUS/1485/2023). 
Informed consent 
The adolescents will receive oral and written information about the study. Informed consent from the 
adolescent will be obtained digitally after the self-evaluation at baseline. While all adolescents are asked to fill 
in the survey forms, only the digital survey data of those adolescents who provide informed consent to 
participate in the study will be stored and used for research purposes. For those whose age at baseline is below 
15 years, a caretaker’s informed consent is necessary; data without caretaker’s consent within 2 weeks of 
adolescent consent will not be stored. The consenting adolescents will have an option to decline and withdraw 
from the study at any point afterwards by sending an SMS, by email, or by using a link on the study site. 
The caretakers and therapists receive both oral and written information about the study. They will provide 
informed consent digitally before being provided the digital survey. Separate consent to the caretaker survey 
will be requested from all caretakers, independent of the age of the adolescent. 
Funding 
This project was funded by the strategic research council of Finland for the consortium Improving mental 
wellbeing as a means of increasing inclusion of young people (IMAGINE) (#353049 Outi Linnaranta, #352702 
Johanna Lammintakanen, #352701 Päivi Berg, # 352700 Jari Lahti, and #353048 Klaus Ranta). Erkki 
Heinonen acknowledges the support of the Finnish Cultural Foundation, the Päivikki and Sakari Sohlberg 
Foundation, and the Social Insurance Institution (KELA).  

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Conflict of interest 
Tarja Koskinen is an accredited IPT-A, IPC-A psychotherapy trainer (IPT-A, IPC-A). Max Karukivi, Tarja 
Koskinen, Klaus Ranta and Jari Lahti are accredited CBT psychotherapy trainers. Klaus Ranta, Mauri 
Marttunen and Outi Linnaranta have received author subventions from Duodecim for articles and as editors or 
authors in a book on IPT-A and IPC-A (published in 9/2023) and a book on Psychiatry. The other authors 
report no financial relationships with competing interests. 
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