This pre-post single group feasibility study, with an embedded survey and a series of stakeholder consultations, was conducted between March and July 2022. Participants were recruited from three services: one child and adolescent mental health service, one school and one charity, in the North of England. Our eligible population was young people aged 12 to 18 years with mild-to-moderate depression. Eligibility was defined by a T-score of ≥65 on the depression subscale (10-items) of the Brief Revised Children's Anxiety and Depression Scale [RCADS-25 (19)]. Young people for whom secondary/specialist care was a more appropriate option (e.g., due to risk of suicide, severe depression, learning disability) did not participate in the study but were signposted to appropriate local services by the research team.

Within recruiting sites, professionals provided potential participants with study information sheets, an expression of interest form, and the RCADS-25 depression subscale. Those interested returned their completed expression of interest form and RCADS-25 questionnaire to the research team who confirmed eligibility. A baseline meeting (either face-to-face or online) was arranged with those eligible. Here, fully informed written assent/consent was obtained (alongside parental consent if a young person was ≤15 years old), and young people were asked for some basic demographic information (i.e., age, sex, ethnicity, religion, family circumstances and education or work).

All young person participants completed the following self-report questionnaires with a researcher at week 0 (baseline) and at 8 weeks post-baseline (follow-up).

Revised Children's Anxiety and Depression Scale—25 item [RCADS-25 (19)]: A condensed version of the original 47-item (20), the RCADS-25 assesses depression and anxiety and has been validated as a self-completed measure for 8–18-year-olds. The RCADS-25 has subscales that capture symptoms across six domains: one domain is depression (10 items) and five domains relate to different anxiety problems (15 items). All items are rated on a 4-point Likert-scale from 0 to 3, where 0 = Never, 1 = Sometimes, 2 = Often, and 3 = Always. Raw scores are transformed into T-scores with higher T-scores denoting greater clinical need. We report T-scores for the RCADS-25 with clinical cut-offs of: 0–64 non-clinical range, 65–69 sub-clinical range, and ≥70 clinical range. The clinical cut-offs are the same for the depression and anxiety subscales (21).

The RCADS-25 was our primary outcome measure and was selected because it is a nationally recommended outcome measure as part of the Mental Health Services Dataset (MHSDS) in the UK. It is routinely collected by professionals within clinical services with children and young people and it is used by commissioners for service evaluation and benchmarking. Therefore, our findings can be interpreted in the context of UK national datasets for our population.

Children's Depression Rating Scale-Revised [CDRS-R (22)]: A 17-item researcher-administered interview widely used in clinical research as a validated measure to assess severity of, and change in, depression symptoms in children and adolescents (23). The CDRS-R covers seventeen symptom areas (e.g., dysfunction, interpersonal relationships, psychosomatic complaints) with items scored on a 1–5 or 1–7 scale. We report raw scores which range from 17 to 113, with higher scores denoting more depressive symptoms. Scores ≤34 suggest no depression, a score between 35 and 40 suggests emerging or early depression (24) and scores >40 indicate diagnosable depression (23).

Behavioural Activation for Depression Scale- Short Form [BADS-SF (25)]: A 9-item questionnaire, based upon the longer 25-item BADS (26, 27), that measures levels of activity on 2 subscales: activation and avoidance. All items, based on the previous week, are rated on a seven-point scale ranging from 0 (not at all) to 6 (completely) with total scores between 0 and 54; higher scores represent increased behavioural activation. Although not currently validated with adolescents, we used the BADS-SF as there are no alternative similar tools available.

Child Health Utility-9 Dimensions [CHU-9D (28)]: The CHU-9D is a self-complete paediatric generic preference-based measure validated for young people aged 7–17 years (29). It was used in the place of the conventional EQ-5D to derive utility values for estimating quality-adjusted life years (QALYs). This was because the youth version of EQ-5D does not have a validated UK tariff and the adult version is not validated in adolescents. The questionnaire assesses functioning “today” across 9 domains (worry, sadness, pain, tiredness, annoyance, school, sleep, daily routine, and activities), each of which has 5 levels (scored 1–5, 1 as best, 5 as worst). Each level has a tariff value smaller than 1 estimated based on population survey (30). For example: in the sadness domain, 1 = I don’t feel sad today (0), 2 = I feel a little bit sad today (0.420), 3 = I feel a bit sad today (0.0455), 4 = I feel quite sad today (0.0722), 5 = I feel very sad today (0.0722). Once all 9 domains are complete, the tariff values of selected levels of them are extracted from 1 (a full utility). The resulting utility value ranges from 0.3261–1, where 1 is perfect health and death is anchored on 0. Utility values at multiple time points are used to estimate QALYs using area under the curve approach (31) and assuming linear changes between time points.

Resource Utilisation Questionnaire for Adolescents (RUQ-A): The RUQ-A was developed by us specifically for this study to collect quantities of use of primary (e.g., GP, practice nurse, etc.), secondary (e.g., A&E, inpatient, outpatient, etc.), community- (e.g., CAMHS team, community paediatrician, social worker, etc.) and school-based (e.g., school nurse, teacher, etc.) healthcare and social services by participants over the preceding 8 weeks via self-report. The scope was based on the reference case for a formal economic evaluation by NICE (32). The initial version collected the use of these services separately for mental health and physical health. Following its completion with the first four participants, we made two amendments to the RUQ-A based on their feedback: merged questions about mental and physical wellbeing, i.e., not differentiating between the two, and adding a question about medication. The amended version included 4 questions for healthcare and social services use and one for days absent from school, training or work. Participants were asked to report the number of times they consulted with the listed professional roles or services in primary and community settings (including at school, in CAMHS, at hospital and private settings) and the respective number of times, average duration, and any out-of-pocket payments (for private settings only). Free text was provided for each question if the service they used or professional consulted with was not on the list. The last question asked participants the number of days they missed from school, training or work as well as the number of days their carers took off work to care for them. The listed items in questions were informed by a literature search of questionnaires previously used in economic evaluations in this population and by previous RUQs developed by our team for mental health interventions. The results were used to identify the frequently accessed services so the collection of this data could be streamlined in the full RCT.

Our BA manual was designed for use by young people and their supporting professionals and parents/guardians and was informed by McCauley et al's (6) clinician's guide among other available BA resources. We have singled out McCauley et al's (6) guide because its application has the best published evidence in terms of the feasibility, acceptability and clinical outcomes of BA for young people to-date. We have developed our BA manual “de novo”. This was for three main reasons: (a) it focuses on adolescents with mild-to-moderate presentations of depression, (b) it can be delivered by non-specialists in community settings (c) it is a single point of reference for young people, parents/guardians and professionals (rather than having different versions of it for each audience).

The manual was divided into 5 modules: Module 1-Starting Up, Module 2-Getting Active, Module 3-Building Skills, Module 4-Overcoming Obstacles and Module 5-Moving Forward. The manual was not a self-help book, but the young person worked through the modules with support from a professional. Each module could be completed in one session, or it could be done in two or more sessions. The modules had two key components: “Things to Know”—information about key concepts and strategies of Behavioural activation (BA)—and “Things to Do”—practical activities that could take place either in-session with the professional or between sessions as “take-away activities”.

BA sessions were delivered face-to-face or online via a secure NHS platform. All participants were offered up to 8 weekly sessions of BA, each lasting between 30 and 45 min. Each session followed the manual for both in-session and between-session work. The young person could attend these sessions with a parent/guardian or another trusted adult who could offer them practical and emotional support outside the sessions.

Professionals were offered weekly supervision in a flexible format: one-to-one or in a group, in person or online. All professionals received a full day's training either in person or online via Microsoft Teams, in addition to completing self-directed learning through an online Massive Online Open Course [MOOC (33)].

Professionals were asked to keep a written record of all BA sessions, noting whether the session took place or was missed, how long it lasted, what activities were completed, whether there were any adverse/serious adverse events reported during the session. The professionals also tracked between-session communications with young people or their parents (e.g., why and how they made contact and the outcome of the communication).

There is limited guidance about the optimum sample size for feasibility studies (34). Julious (35) recommends, as a rule of thumb, recruiting a minimum of n = 12 for a single-group feasibility study. We aimed to recruit n = 15 young people, slightly inflating the number recommended by Julious (35) to account for possible attrition.

We reported the number of people who took up the invitation and consented to participate in the study, the number of participants who completed the intervention or withdrew, and the number of those who completed follow-up measures. We also reported data missingness in the questionnaires. We calculated three sets of T-scores for each participant on our primary outcome measure (RCADS-25): the overall score and the depression and anxiety subscale scores. Using established clinical cut-offs for the RCADS-25 scale, we assigned each participant to one of three groups based on their T-score: A = non-clinical (scores 0–64), B = sub-clinical (scores 65–70) and C = clinical (scores 70+) (21). For the CDRS-R, we reported both the continuous raw scores and the group to which each participant belonged to, based on their scores using the CDRS-R cut-offs: A ≤ 34 = no depression, B = 35–40 emerging/early depression, C > 40 = diagnosable depression.

We created scatterplots to visually present the direction of change in the outcome measures based on the difference in scores from baseline to follow-up. We created bubble-plots to visually present the transition of participants from one group to another (e.g., from clinical to sub-clinical depression). We calculated the means and standard deviations of the RCADS-25 T-scores and CDRS-R raw scores in our sample as an indication of the average severity of depression at baseline and at follow-up. As this was a feasibility study, we did not conduct statistical analyses to measure effects, but we used the term “direction of change” as an indication of the potential effect of the intervention that could justify a follow-up RCT. The terms “positive” and “negative” direction of change do not imply statistically or clinically significant change.

Using research team records, the operating costs of the BA were calculated in Pound Sterling 2022 price and presented by cost elements. RUQ-A data were used to identify the main services associated with depression for NHS and non-NHS organisations that were accessed by participants. The results, alongside participant feedback, were used to inform the revision of the RUQ-A for use in the future RCT. The CHU-9D was used to measure health-related quality of life but given the short observation period, quality-adjusted life years were not calculated.

We created a short survey hosted on the Qualtrics Platform to gather information about the types of support available to young people with depression in different settings, the professionals responsible for providing this and to determine the extent to which BA was already being used. The survey was distributed to professionals within approximately 40 organisations in the North-East of England working with young people within specialist mental health services, mainstream and special schools, NHS Talking Therapies, voluntary agencies and youth organisations.

Ahead of the feasibility study we identified three key stakeholder groups—young people (aged 12 to 18 years as per the recruitment group) with lived experience of low mood/depression, parents/guardians of children with such lived experience, and professionals with experience of delivering low-intensity psychological interventions. The young person and parent/guardian groups were identified from several local Patient and Public Involvement and Engagement (PPIE) organisations/networks as well as our study sponsor's PPIE register. Professionals were identified from the professional networks of the study team. Our stakeholder consultations were critical to the development of the format and content of the BA as well as informing the design of key documentation for the feasibility study.

We completed two rounds of consultation with our stakeholders, either online or in person. All consultations included an initial presentation on the core intervention and study materials which were then discussed as a group. The first round included workshops with the three stakeholder groups (three professionals, four young people and three parents/guardians) where we gathered feedback on drafts of the BA manual, the RUQ-A, participant information sheets and assent/consent forms for use in the feasibility study. The feedback received helped in shaping these key materials, with the subsequent changes reported back in our second round of consultations. During this second round, our three stakeholder groups also provided feedback on some newly devised content in the BA manual, plus a new question about medication added to the RUQ-A.

Our sample included 20 young people aged 12–18 years (M = 14.9, SD = 1.6), recruited over 5 months (February-June 2022) from three sites: an NHS service, a school and a charity. They were predominantly British (i.e., identified as English, Welsh, Scottish or Northern Irish), except 4 participants who identified as: White and Asian, Pakistani, Bangladeshi and African. Just over half of the sample (n = 11) were not affiliated to any religion (agnostic or atheist), 6 were Christians, 2 Muslims and 1 Hindu. All young people lived with their parents, and most were female (n = 17). Our participants attended secondary school (n = 14) or were in further/higher education (n = 6); only 5 were concurrently working (1 full-time, 4 part-time). The baseline RCADS-25 T-scores (based on the depression sub-scale) ranged from 65 to 80, but, on average, the sample scored above the threshold for likely clinical depression (M = 72.5, SD = 5.5). All information is depicted in Supplementary Table S1.

Overall, five professionals delivered the BA and were based within one school, one charitable organisation, and one child and adolescent mental health service. The professionals included a school counsellor, a senior children's wellbeing practitioner, an art therapist and 2 trainee children's wellbeing practitioners. Most (n = 4) were female and aged between 25 and 34 years (n = 4).

All young people who were invited to participate consented to do so and all participants completed baseline and follow-up measures. All but one participant received the intervention. The one participant who withdrew prior to receiving the intervention was at the clinician's suggestion (BA was not deemed to be the most suitable course of treatment for this young person); they still completed outcome measures at follow-up. No data was missing from any of the completed baseline and follow-up questionnaires.

Among the 19 participants who received BA, the mean number of sessions attended was 7.4 (SD: 1.5), ranging from 2 to 9 sessions per person and the mean duration per session was 39 min (SD: 4 min). Over half of the participants (n = 11) attended their sessions as planned without any cancellations, whereas for the rest the mean number of cancelled or “no-show” sessions was 1.2 (SD: 2.0). For most participants (n = 14) sessions took place every 7–10 days, for 1 participant, sessions occurred every 11 days on average, and for another 3 participants the frequency of sessions was more than one per week. One participant was an outlier, having had only 2 sessions over 3 months (92 days). In total, participants on average spent 286 min (SD: 63 min) over the course of delivery.

The time practitioners spent in direct contact with the young people during BA sessions is reported above. In addition, practitioners spent an average of 103 min (SD = 57 min) preparing for sessions and 130 min (SD = 41 min) doing administrative tasks (e.g., writing notes). For cancelled/not attended sessions, professionals still spent time on preparation (M = 13 min, SD = 26 min) and administration (M = 11 min, SD = 20 min). No adverse nor serious adverse events were reported during the feasibility study.

The lack of severity cut-off scores on the RCADS 10-item depression subscale made it difficult for us to differentiate between mild-moderate and severe depression at the point of screening for eligibility to enter the study. Consequently, we added the 9-item Patient Health Questionnaire for Adolescents [PHQ-9A (36)] as a screening tool, in addition to the RCADS-25. If a young person scored ≥15 or gave answers indicating suicidal thoughts based on items of the PHQ-9A, we invited them to a clinical interview to assess depression severity and risk. If the clinical interview judged that the depression was mild-to-moderate, then the young person was invited to participate in the study; otherwise, the clinicians signposted or referred the young person to an appropriate service.

Nine professionals attended the BA training with staff time costs estimated at £1,157 for the attendees and £510 for the two trainers. Three moderators addressed questions and comments during the first 3 weeks of the MOOC launch, costing £2,700 overall. The staff costs of the nine professionals completing the MOOC were £1,157, assuming all completed it according to schedule.

Supervision was held nine times; six were individual sessions and three were group sessions attended by two professionals. Most supervision sessions were conducted via MS Teams and lasted one hour, except for one lasting 30 min. The staff time costs of supervision were £447 for both professionals and the trainer. In total, training and supervision costs were estimated at £5,971, 65% of which were accounted for by the time spent on the MOOC.

In total, 140 sessions were delivered, associated with 172 h of staff working time. The mean total working time spent for the 19 participants who attended sessions was 9.1 h (SD: 2.2 h), ranging from 2 h to 13.5 h. The mean staff time costs of sessions were £207 (SD: £79) per participant.

The usual care survey was open for completion between November 2021 and March 2022. Overall, 21 professionals responded to the questionnaire which was circulated to 40 services within the North-East of England. The services to which respondents belonged included voluntary/charitable organisations (n = 13), the NHS (n = 5), schools (n = 1), a charity partnered with the NHS (n = 1) and the local authority (n = 1). Respondents noted that, in their day-to-day practice, as little as 10% and as much as 80% of the young people whom they support would experience low mood. Where services had to signpost young people with low mood to alternative sources of support the reasons given for this were: having other organisational priorities, considering the depression too severe or complex, having a lack of appropriately trained staff and having limited staff availability.

Usual care took place over 1–10 sessions, usually between 30 min and 1 h, and included: general education, Interpersonal Therapy (IPT), Cognitive Behavioural Therapy (CBT), Behavioural Activation, counselling, pastoral support, psychotherapy, family therapy, emotional wellbeing support, art/drama/play/music therapy and youth work. Interventions were delivered face-to-face, by phone or online, both individually and in groups. Session frequency varied from weekly and monthly to ad-hoc/as needed. Staff were assistants and support workers (e.g., family support workers, teaching assistants, emotional literacy support workers), professionals trained in counselling, low intensity interventions (e.g., psychological wellbeing practitioners) and specialist high intensity interventions (e.g., CBT therapists, family therapists).

Increasing demand for mental health care, but limited staff capacity, have led to high entry thresholds for child and adolescent specialist services, which prioritise severe and complex clinical presentations; therefore, young people with mild-to-moderate problems, including depression, need to access help outside specialist services. This study assessed the feasibility of delivering BA within community settings to inform a large RCT that will test BA's clinical and cost-effectiveness. Two rounds of stakeholder consultations, as well as feedback from the professionals, researchers and young people who took part in the study, helped us refine the intervention materials, data collection tools and research processes.

Our excellent recruitment and retention rates showed that young people with mild-to-moderate depression are willing to take up and complete BA in a school, an NHS service and a charity, supported by professionals from different backgrounds and with different levels of expertise. This is in line with previous research in adult populations (7, 9) which have shown that BA can be supported by a diverse workforce, including more junior mental health workers. Furthermore, these studies have shown that junior mental health workers can achieve similar results at a lower cost than senior therapists (7, 9).

A feasibility study is not designed to test clinical effectiveness, but it can give a signal as to whether a follow-up RCT is worthwhile based on the direction of change from baseline to follow-up. Scores changed in a positive direction for around three-quarters of our participants across all outcome measures. When considering diagnostic cut-offs, the transition from clinical or sub-clinical to non-clinical status was more pronounced for the RCADS-25 than for the CDRS-R, and for depression than for anxiety.

It is noteworthy that “no change” in the clinical status for anxiety was observed among participants whose anxiety was within the “non-clinical” range at baseline, inferring a floor effect. It is unsurprising that the positive direction of change for anxiety was not as prominent as that for depression, given that our sample was recruited based on depression symptoms and the intervention itself was designed for depression. Still, we observed a positive direction of change for those participants whose anxiety scores were above the clinical threshold.

Overall, the data gathered in the RUQ-A was as we expected; healthcare and social service use mainly fell on school and primary care settings. This was anticipated in the development of the measure, as our study population—young people with mild-to-moderate depression—spend most of their time in school and their condition is not severe enough to typically warrant secondary care or medication. We have nevertheless added a question into the RUQ-A to explore medication use. In a future RCT, questions about medication use and secondary care access can be kept brief.

The survey findings demonstrated the variability in the types of support and the different levels of interventions offered to young people with depression; most importantly, the findings reassured us that BA was not widely used in community sites, therefore usual care was a suitable comparator for BA in a future RCT. The survey also showed the wide range of professionals responsible for providing support and interventions in different settings. These findings concur with previous studies in which pathways of mental health care for children and adolescents are loosely defined and inconsistent across different services and community settings (37–40). A future RCT needs to tailor training and supervision to the care pathways and professional skillset in each community setting, considering where our intervention aligns with existing practices and where therapists need to adapt to a new way of working.