Patients’ perspectives on implementing fixed and flexible variants of blended therapy in routine care: A qualitative study of the project PSYCHOnlineTHERAPY

Study design of PSYCHOnlineTHERAPY

Patients in the three-armed cluster-randomized controlled PSYCHOnlineTHERAPY study were recruited between January 2021 and April 2023 via 75 licensed outpatient psychotherapists in Germany (Baden-Wuerttemberg) who delivered the intervention and had been randomized to one of two versions of BT or standard CBT. As part of the recruitment process within routine care, participating psychotherapists screened their patients for eligibility and informed them about the study. Included patients were at least 18 years old and had a psychotherapist-diagnosed depressive and/or anxiety disorder according to the International Classification of Diseases (ICD-10). ³⁶ Self- and observer-based assessments with online-questionnaires and clinical telephone interviews were conducted at several time points, with depression and anxiety severity (Patient Health Questionnaire Anxiety and Depression Scale, PHQ-ADS) ³⁷ at 18 weeks post-inclusion (post-treatment) as the primary outcome.

Interventions

Two versions of BT (PSYCHOnlineTHERAPY_fix, PSYCHOnlineTHERAPY_flex) combined FTF sessions with a psychotherapist and self-help online sessions, and were accessible on the online platform eSano.^38,39 The study treatment of both versions comprised up to 16 sessions in total but could be concluded earlier, e.g., if the therapeutic goals were achieved before reaching this maximum. PSYCHOnlineTHERAPY_fix (FIX) patients were intended to receive a fixed alternating sequence of up to eight FTF sessions and up to eight online sessions. PSYCHOnlineTHERAPY_flex (FLEX) patients were intended to receive up to 16 FTF sessions and up to 16 online sessions with a flexible number and order determined by the therapist and their respective patient (e.g., 11 FTF sessions and five online sessions). CBT-based online sessions were assigned by the on-site therapist, who could choose from seven depression-specific sessions, seven sessions for each anxiety disorder, 22 transdiagnostic sessions, one introductory, and one closing session. The online sessions had an intended duration of 45–60 minutes each and comprised textual, audio, and video material, interactive elements, homework assignments, and downloads (e.g., worksheets). The CBT-based FTF sessions did not follow a predefined treatment protocol within the study.

Participants and recruitment

We aimed to achieve sufficient theoretical data saturation for the qualitative interviews, with a predefined target sample size of n = 20 patients per study group ³⁴ based on established principles. ⁴⁰ Between December 2021 and August 2022, 85 (FIX: n = 42, FLEX: n = 43) of 274 patients already enrolled at this time of the trial were invited to participate in qualitative interviews. Written informed consent was obtained of all study patients at baseline. Study patients were invited if they (a) belonged to either the FIX or the FLEX study group according to the randomization condition assigned to their therapists, (b) had completed the post-treatment assessment (as an indicator of treatment completion), (c) consented to audio recording during the interviews, and (d) had not withdrawn from the main study. Patients who started the intervention before April 2021 were excluded from participating in this qualitative study to avoid bias due to technical issues with the online platform before that date. Invitations were sent via e-mail, directing patients to book an interview appointment on an online booking page. Patients were reminded up to three times via e-mail and up to one time via phone. We recruited 20 patients from the FIX group and 22 from the FLEX group (response rate of n = 42/85, 49.4%). Two FLEX patients were excluded due to technical problems that prevented the audio recording of their interviews. All patients received 30€ for participating in the qualitative interview.

Qualitative data collection

A semi-structured interview guide was developed (TS, IT, AZ), drawing partly on our considerations of potential blending scenarios related to our research questions and partly on the Efficiency Model of Support. ⁴¹ The Efficiency Model of Support was selected as the theoretical basis for our research, as it explains the outcomes of technology-based interventions based on both technological characteristics and characteristics of the interaction between participants and guidance providers (in our case, the on-site therapists). The model encompasses five categories of factors assumed to influence an intervention's effectiveness: factors regarding (a) the alignment of the intervention with the participants’ needs (fit), (b) participants’ intention or motivation to use the intervention (engagement), (c) integration of the intervention into participants’ daily lives (implementation), (d) correct application and use of the intervention (knowledge), and (e) the intervention's user-friendliness (usability).

The self-developed interview guide (see Additional file 2) consisted of 54 open questions from 12 topics: motivation and expectations (three questions); active components, mechanisms of change, and effects (two questions); characteristics of the treatment with online sessions (four questions); characteristics of the treatment with FTF sessions (seven questions); characteristics of blending (nine questions); blending rhythm (six questions); negative effects (four questions); fit (four questions); engagement (five questions); implementation (five questions); knowledge and usability (four questions); further comments (one question). Table 1 shows exemplary questions for each topic. Two questions regarding session ratio and frequency were tailored to the patient's study group (FIX or FLEX). Other than these, all patients were asked the same set of questions.

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Table 1.

Example questions of the interview guide.

Topic	Example question
Motivation and expectations	What specific benefits did you expect from the blended therapy compared to standard psychotherapy?
Active components, mechanisms of change, and effects	What changed for you as a result of the blended therapy?
Characteristics of the treatment with FTF sessions	What did you experience as unique and special about the FTF sessions?
Characteristics of the treatment with online sessions	What type of treatment did you receive in the online sessions that would not have been possible in the FTF sessions?
Characteristics of blending	How would you describe the interplay of the online sessions and FTF sessions?
Blending rhythm	Using your own words, how would you describe the order and ratio of the FTF sessions and online sessions in your therapy?
Negative effects	What short- and long-term negative effects—such as side effects, risks, unwanted events, and experiences—did you encounter as a result of the blended therapy?
Fit	How did the blended therapy suit you and your life situation?
Engagement	How did you manage to keep up with the blended therapy?
Implementation	What helped you implement the blended therapy in your everyday life?
Knowledge and usability	Which difficulties did you encounter during the therapy when using the online platform?

The interviews were conducted via phone between January 2022 and August 2022 by two psychologists with university-degrees and in CBT training (JF, LM) who received specific training for this task by the responsible study team members (TS, AZ). On average, the interviews lasted 59 minutes (SD = 13 minutes), with durations ranging from 24 to 100 minutes. The audio recordings of the interviews were transcribed verbatim using the software tool MAXQDA ⁴² following a predefined transcription guide. All qualitative data were anonymized during the transcription process.

Quantitative data collection

Quantitative data were collected through online questionnaires and diagnostic interviews at baseline, prior to the start of the intervention, as part of the PSYCHOnlineTHERAPY study. ³⁴ Sociodemographic patient data included age, gender, educational level, relationship status, employment status, residence size, and prior psychotherapy experience. Diagnoses were assessed by the therapists for their respective patients. Depression and anxiety severity was assessed with the PHQ-ADS, where higher scores indicate greater levels of anxiety and depressive symptoms (score range: 0–48, α = .89). ³⁷ Data on whether an alternating session sequence (i.e., alternating FTF and online sessions as defined for the FIX condition) was implemented for each patient were derived from standardized therapist reports completed after each FTF session, which also included information on the assigned online sessions. Therapist characteristics were assessed via online questionnaires and included information on age, gender, time since licensed as therapist, and experience with digitally supported psychotherapy. Quantitative data was analyzed descriptively using SPSS. ⁴³

Data analysis

Using the software tool MAXQDA, ⁴² we conducted a qualitative content analysis following a deductive-inductive approach ⁴⁴ with the following procedure: (1) Within the deductive approach, main categories were derived based on the research questions and the topics outlined in the interview guide. (2) Within the inductive approach, subcategories and codes were initially developed by two independent coders (KB, LL). Starting with two interviews, additional transcribed material was sequentially added during this process until a total of 70% (n = 28) of interviews were included for the development of the code system. Existing codes were refined, and new codes were added and discussed during regular consensus meetings (KB, LL, TS). Coding rules were simultaneously developed, defining one sentence as the smallest coding entity, a complete statement as the context entity, and allowing multiple codes for a single text passage. (3) The initial code system, including code definitions and illustrative statements, was refined through feedback loops with CBT-therapists and experts in IMIs and qualitative research (AZ, IT, JS, TS). (4) A second dyad of independent coders (LL, JS) applied the revised preliminary code system to the previously coded 70% (n = 28) of interview material to assess its applicability. (5) The code system was revised in further consensus meetings and additional feedback loops (AZ, IT, JS, TS). (6) A test coding of three interviews (from the 28 interviews) was performed by a third dyad of independent coders (JS, LM), leading to final adjustments of the code system and the coding rules (JS, LM, TS). (7) The independent coders (JS, LM) performed the final coding on the entire dataset (100%, n = 40). (7) The inter-coder agreement with a targeted code overlap of 70% was weak ⁴⁵ to moderate, ⁴⁶ with a Kappa value of k = 0.46. Coders were psychology students (KB, LL, and LM) and a researcher and clinical psychologist (JS), and were trained by the responsible study team member (TS). Frequencies of the final theme codes are reported for the whole sample as well as separately for the FIX and FLEX study groups.

Sample characteristics

The sociodemographic and clinical characteristics of the interviewed sample are shown in Table 2 (see Additional file 3 for details on the non-interviewed sample). The mean age of the 40 interviewed patients was 39.2 (SD = 14.1), with 28 (70.0%) being female. Most patients were in a relationship (n = 30, 75.0%) and employed (n = 31, 77.5%). About half of the sample (n = 22, 55.0%) had a high level of education, and the majority of the patients (n = 34, 85.0%) lived in a small town with less than 20,000 inhabitants. Regarding their diagnosis at inclusion, 20 (50.0%) had a depressive disorder, 11 (27.5%) had one or more anxiety disorders, and 9 (22.5%) had comorbid depressive and anxiety disorders or a mixed anxiety and depressive disorder. The severity of depression and anxiety at baseline on the PHQ-ADS was, on average, moderate (M = 22.5, SD = 9.3). The 22 therapists treating the interviewed patients were predominantly female (n = 16, 72,7%) and had a mean age of 49.1 years (SD = 11.0). The average number of years since being licensed as a therapist was 8.42 (SD = 11.6), with 5 (22.7%) therapists having previous experience with digitally supported psychotherapy.

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Table 2.

Baseline characteristics of the interviewed sample.

Characteristics	IG, interviewed (n = 40/375)	FIX, interviewed (n = 20/40)	FLEX, interviewed (n = 20/40)
Age	39.2 ± 14.1 (18–64)	41.2 ± 15.1 (19–64)	37.2 ± 13.2 (18–60)
Gender
Male	12 (30.0%)	8 (40.0%)	4 (20.0%)
Female	28 (70.0%)	12 (60.0%)	16 (80.0%)
Relationship
Single	10 (25.0%)	7 (35.0%)	3 (15.0%)
Relationship/Married	30 (75.0%)	13 (65.0%)	17 (85%)
Education
Low	18 (45.0%)	10 (50.0%)	8 (40.0%)
Middle	10 (25.0%)	5 (25.0%)	5 (25.0%)
High	12 (30.0%)	5 (25.0%)	7 (35.0%)
Employment
Employed	31 (77.5%)	15 (75.0%)	16 (80%)
Student/apprentice status	3 (7.5%)	2 (10.0%)	1 (5.0%)
Unemployed	6 (15.0%)	3 (15.0%)	3 (15.0%)
Residence
Small town/village	34 (85.0%)	18 (90.0%)	16 (80.0%)
Medium-sized town	2 (5.0%)	0 (0.0%)	2 (10.0%)
City	4 (10.0%)	2 (10.0%)	2 (10.0%)
Prior psychotherapy	27 (67.5%)	13 (65.0%)	14 (70.0%)
Diagnosis (therapist-based)
Anxiety disorder(s)	11 (27.5%)	5 (25.0%)	6 (30.0%)
Depressive disorder(s)	20 (50.0%)	11 (55.0%)	9 (45.0%)
Comorbid anxiety and depressive disordersa	9 (22.5%)	4 (20.0%)	5 (25.0%)
PHQ-ADS (score range: 0–48)	22.5 ± 9.3	22.5 ± 8.8	22.5 ± 10.1

Note. IG = Intervention group, FIX = PSYCHOnlineTHERAPY_fix, FLEX = PSYCHOnlineTHERAPY_flex, PHQ-ADS = Patient Health Questionnaire Anxiety and Depression Scale.

a

including the diagnosis Mixed anxiety and depressive disorder.

Intervention characteristics

Within the FIX group, 70.0% (n = 14/20) of patients received BT with the intended alternating sequence of FTF and online sessions. For the remaining 30.0% (n = 6/20), therapist reports indicated deviations from the intended alternating session rhythm. Within the FLEX group, 10.0% (n = 2/20) had an alternating sequence.

Qualitative findings

The qualitative content analysis resulted in 10 main categories with s = 30 subcategories and m = 163 theme codes. Main categories were: motivation and expectations (s = 2, m = 19); active components, mechanisms of change, and effects (s = 2, m = 14); blending scenarios (s = 8, m = 51); therapeutic alliance (s = 2, m = 7); negative effects (s = 3, m = 11); fit (s = 1, m = 10); facilitators of treatment adherence and engagement and daily life transfer (s = 3, m = 15); barriers to treatment adherence and engagement and daily life transfer (s = 3, m = 9); usability (s = 2, m = 8); and optimization possibilities (s = 4, m = 19). Key themes (m = 88, 54% of 163) mentioned by at least 25% (n ≥ 10) of interviewed patients (regardless of the study group) are reported below and summarized in Table 3 with definitions, frequencies (for the total sample and separately for FIX and FLEX), and supporting quotations. A complete listing of all m = 163 theme codes with their frequencies, definitions, and supporting quotations can be found in Additional file 4.

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Table 3.

Key themes^a of the qualitative content analysis with frequencies, definitions, and supporting quotations.

Main category	Subcategory	Code	Interviewed patients (n = 40)		Definition	Supporting quotations
			n total (FIX/FLEX)	% total (FIX/FLEX)
Motivation and expectation	Motivation to participate and positive expectations	Participation reinforcement by therapist	25 (15/10)	63 (75/50)	The therapist showed behavior to reinforce the patient's motivation to participate, pointed out the benefits of participation, recommended participation, or provided information on BT.	“The combination treatment was suggested to me by my psychotherapist because she thought it made sense in view of my symptoms. I then registered.“ (P6)
		Interest in the treatment format	18 (9/9)	45 (45/45)	Patients expressed their interest in BT or their openness to trying out the new treatment format.	“I'm honestly open to new things. My therapist also explained everything to me, that it was a new approach or at that time still a pilot project. (…) And that made me quite curious.” (P18)
		Location- and time-independent use of OS	18 (7/11)	45 (35/55)	Patients expected that OS can be used independent of time and location so that they could plan them independently in line with their own needs and at their own pace, without having to make appointments with their therapist and/or be at a specific location.	“Above all, the flexibility in terms of time, so that I can do the (…) sessions whenever I want and that I can (…) take the time for them whenever I want.” (P7)
		Independent work on therapy content at home	17 (8/9)	43 (40/45)	Patients were interested in the opportunity to work independently on therapy content at home and expected positive effects through self-activity, such as better progress in therapy.	“I was motivated to also work a little bit on something on my own and to read and such.” (P22)
		Intensified and enriched therapy experience through blending	15 (7/8)	38 (35/40)	Patients expected a quantitative and qualitative intensification of the treatment through the combination of OS and FtF sessions with a mutual enrichment of both elements as well as an extension of the treatment and a deepening of therapy content through the combination.	“I get a lot more input and can work on myself much more than in a normal therapy.” (P12)
		Improvement of mental health symptoms	11 (5/6)	28 (25/30)	Patients expected or hoped for the improvement in their psychological symptoms (e.g., depression, anxiety) and that they would receive necessary treatment for existing symptoms, psychological distress, or perceived problems.	“To get something faster and better that you can use to maybe alleviate the symptoms.” (P36)
		OS enable psychoeducation and deepening of content	10 (2/8)	25 (10/40)	Patients expected psychoeducation to be a part of the OS and that they would learn about their illnesses, symptoms, and background knowledge and receive more in-depth psychoeducational therapeutic content through the OS.	“I was motivated by the hope that I would not only have the sessions but also learn the background knowledge. That means not just having conversations, but also gaining a little bit of background knowledge about the illness.” (P39)
Active components, mechanisms of change, and effects	Active components and mechanisms of change	Practical application exercise	23 (10/13)	58 (50/65)	Patients perceived practical exercises and the active application of therapy content (in their daily lives) as a helpful element in BT.	“The practical exercises I did with my therapist helped.” (P28)
		Psychoeducation	20 (9/11)	50 (45/55)	Patients perceived psychoeducation (e.g., learning about mental disorders or their treatment) as a helpful element in BT.	“I found the explanations most helpful. By explanation, I mean understanding where things come from, why they happen, basically what they are at all.” (P4)
		Cognitive therapeutic techniques	17 (9/8)	43 (45/40)	Patients perceived cognitive techniques (e.g., cognitive restructuring, cognitive reflection of content) as helpful elements in BT.	“What also really occupied me was this guidance through the thought patterns. (…) it was accompanied by many ‘aha'-experiences for me.” (P2)
		Normalization of symptoms	13 (5/8)	33 (25/40)	Patients perceived the normalization and understanding of their symptoms as a helpful element in BT. E.g., realizing that other people are also affected or feeling that they are not alone with their mental health disorder.	“Hearing that it's not totally unusual (…), that explanation that these are partly normal feelings and reactions to events (…), that definitely (…) helped, I believe.” (P7)
		Blending of OS and FtF sessions	11 (6/5)	28 (30/25)	Patients perceived the blending of OS and FtF sessions, such as their interaction, their mutual reference, or the fact that the contents complemented each other, as a helpful element in BT.	“I think I made faster progress, too, because it's a combination of working on things myself and then discussing them with the therapist. Then understanding them completely. Then starting all over again and then with the therapist again, and so on and so forth.” (P17)
		Therapeutic alliance	10 (5/5)	25 (25/25)	Patients perceived the working alliance and the relationship with their therapist as a helpful element in BT.	“A very pleasant atmosphere for me (…). It was a truly appreciative, respectful atmosphere too (…), the honesty in the conversations, (…) it was never hurtful, never.” (P2)
	Effect	Behavioral change in daily life	18 (10/8)	45 (50/40)	Patients reported the application of new strategies and behaviors in their daily lives as an outcome of the BT.	“I tried or learned to deal with it in everyday life and simply put into practice what I learn.” (P33)
		Improved coping with symptoms	17 (9/8)	43 (45/40)	Patients reported improved coping with existing symptoms or related situations, mastering of new challenges, or using strategies to manage symptom-related problems as an outcome of the BT.	“How I handle my feelings, especially with depression, has improved significantly.” (P13)
		Symptom improvement	17 (8/9)	43 (40/45)	Patients perceived an improvement in their psychological symptoms (e.g., mood, rumination), a remission or reduction in the symptoms for which therapy was started, or an improvement in their general well-being as an outcome of the BT.	“The anxiety disorder, actually. It was really severe before, but now it's actually really good.” (P11)
		Building understanding of disorder	15 (5/10)	38 (25/50)	Patients perceived the development of a better understanding of their own disorder (e.g., acquiring knowledge, changing their attitude towards their own symptoms) as an outcome of the BT.	“I've gained a different perspective on my anxiety disorder, simply understanding more about what lies behind it, where the anxiety comes from, and what anxiety actually means.” (P26)
		Strengthening of the self-concept and self-esteem	11 (6/5)	28 (30/25)	Patients perceived strengthening of their own self-concept, self-esteem, self-confidence, self-reflection, or paying more attention to their own needs as an outcome of the BT.	“My self-esteem has significantly improved. The way I see myself.” (P13)
Blending scenarios	Characteristics of blending	Discussion of online content in FtF sessions	31 (13/18)	78 (65/90)	Content from the OS was discussed in the FtF sessions, e.g., by clarifying open questions about the online content or debriefing the implementation of the OS and their contents or exercises.	“Then I worked on it at home, and the next time we met, we talked about (…) how it went, what worked, and what (…) didn't work.” (P6)
		Content-related referencing of OS and FtF sessions	27 (14/13)	68 (70/65)	OS and FtF sessions relate to each other in terms of content, the topics are coordinated, they build on each other, or the elements fit together thematically.	“Whenever we had a topic that was currently relevant to me, [my therapist] always made sure to provide me with the appropriate online lessons. This way, it wasn't just random online content, completely unrelated, but [instead] built upon each other.“ (P27)
		Reciprocal enrichment of OS and FtF sessions	14 (7/7)	35 (35/35)	There was a positive reciprocal complementarity between OS and FtF sessions and their respective advantages or characteristics; both elements in combinations were perceived as better than one alone, e.g., by enabling a more intensive, deeper, or effective treatment.	“I think it's good that it's a combination. Having both or being able to do both because I think one without the other might not be as profound or effective. I find both therapy approaches complement each other very well.” (P12)
		Continuing therapy between FtF sessions	11 (2/9)	28 (10/45)	Waiting time between the FtF sessions can be bridged by the OS taking place in the meantime, and there is the opportunity to make further progress between FtF sessions and keep up with the therapy.	“That I always had input at home between [face-to-face] sessions. And also thought-provoking ideas that I could reflect on until the next session.” (P39)
	Blending activities of the therapist	Selection of suitable OS	31 (17/14)	78 (85/70)	The therapist selected suitable and appropriate OS that incorporated topics from the FtF sessions or were experienced as suitable for the individual patients or their situation.	“[My therapist] checked after each of our therapy sessions which topics were most relevant to that day's session and assigned them to me so that after each therapy session with him, I could get further into the content during the online session.” (P12)
		Guidance of OS	30 (17/13)	75 (85/65)	The therapist guided the patient throughout the OS, e.g., by being a contact person for questions or problems, sending reminder messages, checking completed OS, or giving feedback.	“[My therapist] always asked if I had already done it. If I had any problems with [the online sessions]. If he could help me. He also sent me reminder emails to make sure I didn't forget.” (P13)
		Coordination of the BT	16 (7/9)	40 (35/45)	The therapist assumed a coordinating role in the implementation and planning of BT, guiding patients through treatment and maintaining an overview.	“[The therapist] has the role of coordinating these online sessions. He also assigns the therapy topics to the patient, and he can best assess which topic should be worked on next.” (P12)
	Importance of the two elements	FtF sessions more important	21 (10/11)	53 (50/55)	The FtF sessions were perceived as more important than the OS throughout or at some point during the treatment (due to certain characteristics), or the FtF sessions were perceived as the main element and the OS merely as a supplement.	“I would say the appointments with my therapist were more important. I think that was the main element.” (P7)
		Both elements equally important	17 (8/9)	43 (40/45)	Both elements of the BT were perceived as equally or almost equally important, i.e., OS and FtF sessions were equivalent treatment components.	“I think both are equally important because I think it's the interaction that matters, finding that balance between online [session] and therapist.” (P8)
	Characteristics of the FtF sessions	Personal contact	37 (19/18)	93 (95/90)	The personal contact with the therapist was a characteristic of the FtF sessions in the form of direct personal conversations, the availability of a contact person, or the opportunity to talk to someone about the therapy content.	“I just found it nice to talk to someone about my problems (…). Actually, I look forward to it every Thursday because I always think to myself, ‘Now I can talk a bit, (…) just talk a bit about my problems.” (P1)
		Processing of individual topics	31 (17/14)	78 (85/70)	Individual and acute topics and problems could be addressed in the FtF sessions with a high degree of customizability of the FtF sessions and their topics (compared to the OS). In the FtF sessions, the focus is on the individual patient.	“Unique is that one can specifically and individually address the person, so me in this case, address my problems. Yeah, especially the ability to shape each session according to current needs.” (P12)
		Change of perspectives	17 (7/10)	43 (35/50)	In the FtF sessions, patients experienced the possibility that topics can be viewed from different angles and developed new or alternative perspectives on topics.	“Especially the empty chair dialogues, looking at things from different perspectives (…), definitely helped me.” (P7)
		Reflection, deepening, repetition	13 (6/7)	33 (30/35)	In the FtF sessions or following FtF sessions, therapy content was reflected on, deepened, or repeated, or topics were dealt with in more depth than in the OS.	“Deepening topics over weeks and revisiting points that had developed in the meantime, this wasn't possible with the online therapy.” (P7)
		Practical exercises and homework	12 (3/9)	30 (15/45)	In FtF sessions, practical exercises (e.g., relaxation exercises) were learned and implemented or applied in everyday life as a part of homework.	“He also did mindfulness exercises with me and things like that.” (P32)
		Limited FtF session time	10 (4/6)	25 (20/30)	There was a time limit for the FtF sessions, or patients felt that too little time was available in the FtF sessions.	“During a session with the therapist, you're somewhat bound by time because there's already the next patient waiting afterward for something.” (P38)
	Characteristics of the OS	Patient examples	26 (14/12)	65 (70/60)	Normalization of their own symptoms through online content with fictional patient examples as a helpful element to understand their own symptoms, e.g., through examples of other affected persons, the identification with them, and the similarities and differences.	“I would say I had three (..) kindred spirits in [the online sessions]. (…) They sometimes gave me a bit of encouragement; sometimes they gave me guidance on what I should answer or where I should be directed on my further path.” (P25)
		Location- and time-independent flexible use	24 (13/11)	60 (65/55)	Permanent and location-independent availability to use OS and time flexibility, e.g., with the option of taking breaks and deciding independently on the amount of time invested.	“That you essentially had the therapy at home. And you could always access it whenever you felt the need to do the tasks or just read up on something.” (P33)
		Psychoeducation	20 (12/8)	50 (60/40)	Psychoeducation was a part of the OS. E.g., learning about mental disorders and their treatment or dealing with specific topics like depression or anxiety disorders.	“I had the opportunity to gain background knowledge on certain topics (…) connections were also highlighted that weren't always present and clear to me.” (P2)
		Reflection and repetition	16 (7/9)	40 (35/45)	Repetition of content or reflection on one's own thinking or behavior in the context or as a result of the OS, e.g., identification of dysfunctional thought patterns or gaining insights regarding one's own topics through a reflective approach.	“It´s a deeper reflection. Because you revisit those things where you question yourself again, think about them again (…) [you] can work through the whole thing for a longer time.” (P36)
		Variety of media formats	14 (6/8)	35 (30/40)	In the OS, content is presented using various media, e.g., worksheets, videos, audio recordings, texts, or interactive elements.	“Sometimes reading, sometimes audio recordings that you could listen to, and then writing some things yourself (…) I found this variety really great.” (P22)
		Variable duration of processing time	14 (9/5)	35 (45/25)	OS lasted different lengths of time. There were OS that took a long time and OS that took a short time.	“Sometimes (…) one or the other [online session] was too long, too complex. Some I felt were relatively short, and some were quite complex.” (P21)
		Practical exercises	13 (7/6)	33 (35/30)	Practical exercises (e.g., relaxation exercises) were learned and implemented or applied in everyday life as a part of the OS.	“Especially the different exercises. What comes to my mind are the various relaxation techniques. (…) I could listen to them repeatedly and practice.” (P33)
		Lack of personal contact	13 (7/6)	33 (35/30)	There is no personal contact person on the online platform, so no direct personal contact is possible when working on the OS, and a personal conversation with direct feedback is missing (compared to FtF sessions).	“Someone who listens to me (…). It's not possible in an online session that you have someone who can directly respond to your current personal feelings.” (P22)
		Self-directed engagement	12 (6/6)	30 (30/30)	Possibility of independent, active engagement with topics within the OS. Self-organized processing of the OS independently of the therapist.	“I found it important that you could work independently and that you were able to work through some things yourself.” (P28)
		Lack of individualization	10 (6/4)	25 (30/20)	The content of the OS could not be individually tailored to the patients, or only to a limited extent, or they did not fit the individual situation, needs, or wishes of the patients. The topics of the OS were rather general and not specific enough for individual concerns.	“Sometimes I felt it wasn't quite tailored to me.” (P3)
	Implementation of the blending rhythm	Flexible blending rhythm	23 (4/19)	58 (20/95)	There was a flexible frequency of OS and FtF sessions, spontaneous and short-term scheduling of FtF appointments and OS, or no regularity in the blending rhythm. There was a flexible blending rhythm as part of the FLEX study condition.	“[My therapist] suggested a certain number of online sessions and then the rest within the timeframe for face-to-face sessions. And I could (…) schedule the appointments as it suited me, and this flexibility was definitely there.” (P22)
		Regular blending rhythm	18 (16/2)	45 (80/10)	There was a regular, alternating blending rhythm or a blending rhythm according to a specific pattern. The FIX study condition was implemented as predefined, or a regular blending rhythm was applied within the FLEX study condition.	“That was balanced 50–50. After each [face-to-face] session, an [online] lesson followed.” (P37)
		Balanced ratio of OS and FtF sessions	12 (6/6)	30 (30/30)	The ratio between FtF sessions and OS was (approximately) half—half.	“That was actually balanced equally (…) I didn't have more of one and less of the other, but both were equal.” (P33)
	Evaluation of the blending rhythm	Advantages of a flexible blending rhythm	20 (1/19)	50 (5/95)	The patients experienced advantages of a flexible blending rhythm, e.g., the flexible design of therapy to suit individual needs or the possibility for patients to participate in therapy planning. The flexible blending rhythm was perceived as appropriate or well-coordinated, or the patients were satisfied with the flexible blending rhythm.	“I find it more individually tailored to everyone, and it also removes the fear of thinking, ‘Okay, I only have so many sessions left or so much time left.’ It's flexible. If you still need something, then you can still rearrange it.” (P28)
		Advantages of a regular blending rhythm	17 (17/0)	43 (85/0)	The patients experienced advantages of a regular blending rhythm, e.g., the reliable scheduling in therapy or the experienced continuity in therapy. The regular blending rhythm was perceived as appropriate or well-coordinated, or the patients were satisfied with the regular blending rhythm.	“It's (…) the continuity (…) having a fixed appointment every two weeks that provides a bit more structure.” (P7)
	Decision on the blending rhythm	Decision-making by therapist	17 (12/5)	43 (60/25)	Decisions on the frequency and ratio of sessions were (mainly) made by the therapist alone. If necessary, the therapist took into account existing relevant particularities or wishes of the patients.	“My therapist did that. So, I didn't really decide much about it.” (P19)
		Joint decision-making by both	12 (5/7)	30 (25/35)	Decisions on the frequency and ratio of sessions were (mainly) made jointly by the therapist and the patient.	“Always in mutual conversation. (…). We talked, and accordingly, it was determined whether we could do it or not. (..) I would say together.” (P25)
Therapeutic alliance	Facilitators	Positive interpersonal aspects and communication	32 (14/18)	80 (70/90)	Patients perceive the therapeutic relationship or communication with the therapist as positive, with characteristics such as empathy, trust, appreciation, respect, sympathy, interpersonal fit, and positive feelings such as a sense of security in relation to the therapist.	“What worked well was that (…) we never talked past each other. [My therapist] always understood what my current issue was or, let´s say, what I wanted to hear.” (P12)
		Consent to the therapeutic procedures and therapist behavior	14 (8/6)	35 (40/30)	Patients evaluate the therapist's approach or behavior in the FtF sessions or across sessions positively. Wishes and needs regarding the therapeutic procedures were fulfilled, e.g., by allowing sufficient time for the concerns of the patients.	“The goal really is from both sides that I get better. It's not just my goal; [my therapist] genuinely wants to actively help me get better.” (P13)
		Positive organizational and treatment conditions	11 (5/6)	28 (25/30)	Patients found the general conditions and the organization of the FtF sessions to be positive, e.g., because of flexible scheduling or the availability of the therapist.	“Appointment arrangements worked really well. (…) [My therapist] is very open about whether you would like a video call or whether a phone call was enough. Or whether we make an online appointment if it didn't work for one of us at a particular time.” (P36)
	Hindering factors	Negative interpersonal aspects and communication	18 (8/10)	45 (40/50)	Patients report stressful or negative relationship experiences with the therapist, with characteristics such as communication difficulties, misunderstandings, uncomfortable silences, or inhibitions to open up. The interpersonal fit was not given or only given to a limited extent, e.g., due to their own characteristics/expectations or those of the therapist.	“I find it sometimes difficult, perhaps initially on a personal level, to open up to someone who is a stranger.” (P26)
Negative effects	Negative effects of the BT	No negative effects	26 (15/11)	65 (75/55)	The patients experienced no negative effects from the BT.	“I haven't experienced anything negative or any risks.” (P24)
	Negative effects of the FtF sessions	No negative effects	22 (13/9)	55 (65/45)	The patients experienced no negative effects from the FtF sessions.	“I haven't noticed anything negative [in the face-to-face sessions] either.” (P27)
	Negative effects of the OS	No negative effects	22 (14/8)	55 (70/40)	The patients experienced no negative effects from the OS.	“No negative effects.” (P9)
		Emotional distress	13 (7/6)	33 (35/30)	OS caused emotional distress or the activation or intensification of negative emotions (e.g., depressed mood or anger as a reaction to therapy content). Patients experienced frustration from OS.	“Sometimes afterward I was actually a bit irritated. Because when I asked someone for help, and they couldn't really assist me, I felt quite annoyed after that.” (P11)
Fit	Fit	Content tailored to individual needs	26 (14/12)	65 (70/60)	The availability of needs-specific content and the extent to which the therapy content matched individual needs (e.g., in terms of symptoms, comorbidity, or therapy goals) were perceived as a relevant factor in the patient's fit with the treatment.	“I saw myself in those things, what I experience, have experienced, and what concerns me. So (…) it definitely fit very, very well for me.” (P30)
		Indication and contraindication of specific symptoms	21 (9/12)	53 (45/60)	The patient's symptoms or specific diseases or their severity were perceived as relevant factors in the patient's fit with the treatment.	“Someone with a very severe depression can't just sit down and do it. (…) Because participation is required (…) and so the person, well, someone who isn't capable of participating at that moment, can't do the [online] lessons either.” (P25)
		Need for flexibility in treatment	20 (9/11)	50 (45/55)	A need for flexibility in the therapy or the need for additional therapy elements (e.g., more sessions) were perceived as relevant factors in the patient's fit with the treatment.	“Simply because it's very flexible. And it can adapt well to mothers with children or fathers, employed people.” (P36)
		Self-discipline and drive	15 (10/5)	38 (50/25)	Self-discipline and drive, self-motivation, perseverance for therapy in general or for the OS in particular, or the ability or mental capacity to motivate oneself to actively participate in therapy were perceived as relevant factors in the patient's fit with the treatment.	“You really need a certain drive. And that's often not there or hard to come by with mental illnesses. I think for someone who doesn't otherwise get much done, it's also difficult to master tasks.” (P14)
		Basic skills and abilities	14 (7/7)	35 (35/35)	Abilities and skills of the patients (e.g., expressing oneself in writing, concentrating, reading texts), existing learning experiences (e.g., the experience of working something out independently), or needs that go hand in hand with existing abilities were perceived as relevant factors in the patient's fit with the treatment.	“The therapy format is suitable for people who (…) had to work things out on their own in their lives often and also have the ability to reflect on themselves.” (P38)
		Socio-demographic characteristics	10 (4/6)	25 (20/30)	Socio-demographic characteristics (e.g., age, education) or life circumstances (e.g., family situation) were perceived as relevant factors in the patient's fit with the treatment.	“It was sometimes difficult for me with two children (…) to keep the scheduled appointments, especially if one of them got sick or something, and even then, I was still able to do an online session, which was very helpful for me.” (P29)
		Technical knowledge and equipment	10 (6/4)	25 (30/20)	The technical understanding, such as basic PC skills, attitudes towards technology, familiarity with digital tools (also depending on the target group), or the available technical equipment, were perceived as relevant factors in the patient's fit with the treatment.	“There needs to be a basic technical understanding to operate the website. But if that's there, I think it can be beneficial for everyone.” (P13)
Facilitators	Treatment adherence and engagement and transfer into daily life	Guidance by therapist	33 (15/18)	83 (75/90)	Therapeutic guidance, such as motivating behavior, helpful tips, or reminders from the therapist, was perceived as a facilitating factor for treatment adherence and engagement and transfer into daily life.	“[My therapist] always talked openly with me about it. I could ask questions. She gave me the inputs, the possibilities: ‘What do you think? Do you see anything for yourself there?” (P20)
		Self-discipline and drive	29 (13/16)	73 (65/80)	Self-discipline, self-motivated processing of (online) content, active, independent planning of therapy elements, or independently overcoming internal barriers were perceived as facilitating factors for treatment adherence and engagement and transfer into daily life.	“I just wanted to implement and follow through on it myself. So, I didn't have to force myself each time. I really did it on my own initiative.” (P33)
		Hope for improvement	20 (12/8)	50 (60/40)	The expected change or improvement through the intervention, the striving for health or the improvement of one's own life situation, or the existing motivation for change and the treatment as an opportunity to change something were perceived as facilitating factors for treatment adherence and engagement and transfer into daily life.	“Yes, I think my motivation. So, that I wanted to get out of the depression again.” (P18)
		Symptom improvement and therapy achievements	14 (6/8)	35 (30/40)	A sense of achievement in therapy or the experience of symptom improvement, acute relief, or general well-being as a therapeutic effect were perceived as facilitating factors for treatment adherence and engagement and transfer into daily life.	“When you noticed that you were entering a difficult phase again and the online modules were helpful. Then it was clear that you would use them more frequently or that you would tune in exactly at that time.” (P36)
		Location- and time-independent flexibility	14 (8/6)	35 (40/30)	The location- and time-independent flexibility, e.g., flexible scheduling of therapy sessions or flexible access to OS, was perceived as a facilitating factor for treatment adherence and engagement and transfer into daily life.	“For the modules (…), it was actually helpful that you could essentially do them at any time, whether day or night.” (P14)
		Structuring treatment elements and processes	14 (9/5)	35 (45/25)	The regularity of sessions or schedules and the resulting structure or the predictability in the blending rhythm were perceived as facilitating factors for treatment adherence and engagement and transfer into daily life.	“The combination of flexibility but also fixed appointments. That was a good combination for me, that it's not all flexible and yet you have fixed elements.” (P7)
	Treatment adherence and engagement	Feeling of commitment	11 (6/5)	28 (30/25)	A feeling of commitment, e.g., through the perceived need to fulfill requirements or expectations or agreements with the therapist (regarding the processing of OS), was perceived as a facilitating factor for treatment adherence and engagement.	“It was the knowledge that I should get it done because it was agreed upon after all.” (P14)
	Transfer into daily life	Learning and applying practical exercises	20 (9/11)	50 (45/55)	Practical exercises (e.g., relaxation exercises, breathing exercises) and practicing or implementing strategies that were learned in therapy and that can easily be applied in daily life were perceived as facilitating factors for transfer into daily life.	“I had many opportunities to apply [the practical exercises], and I also always remembered them when I was in the situation, not always all the strategies, but those that I liked the most, and I was able to apply them very well.” (P4)
		Use of therapeutic material	11 (5/6)	28 (25/30)	The use of written therapeutic materials, such as worksheets or psychoeducational material, was perceived as a facilitating factor for transfer into daily life.	“Having an actual piece of paper in front of me that was at a place where I passed by frequently every day and my gaze fell upon it, I could be reminded of what I could practice or implement.” (P2)
Barriers	Treatment adherence and engagement and transfer into daily life	Limiting time resources and life circumstances	18 (8/10)	45 (40/50)	Difficulties regarding the required or available time resources or their management, life circumstances, or events and related daily demands and priorities were perceived as barriers for treatment adherence and engagement and transfer into daily life.	“Yes, the time aspect. Because the [online] modules were longer, I was relatively exhausted afterward, and I had little time since I was under a lot of stress at school. This occasionally prevented me from dealing with it right away or within a week.” (P13)
		Lack of drive	16 (10/6)	40 (50/30)	A lack of personal drive, difficulties in motivating oneself and actively applying therapy content in daily life, or fluctuating self-motivation were perceived as barriers for treatment adherence and engagement and transfer into daily life.	“When the energy wasn't there, I was inside my head. (…) I knew about the tasks, but my body said, ‘We're not doing anything today, I can't today, I don't want to’, it was stuck.” (P5)
		Symptom-related difficulties	13 (7/6)	33 (35/30)	Existing or newly emerging symptoms, such as behavioral patterns associated with the existing illness, were perceived as barriers for treatment adherence and engagement and transfer into daily life.	“Actually nothing, but of course, when I was depressed, everything seemed more difficult because everything felt so exhausting, and it feels hopeless. And yeah, then you just have those phases.” (P24)
	Transfer into daily life	Difficulties in implementation of strategies	14 (6/8)	35 (30/40)	The application of strategies could not be established in daily life, exercises were not or only temporarily carried out at home, or the application of the strategies was not successful (e.g., due to a lack of knowledge), which was perceived as a barrier for transfer into daily life.	“Some exercises were easy to implement, but some other exercises were sometimes a bit inconvenient, and it sometimes took some effort to actually do the exercises.” (P12)
Usability	Facilitators	Independent coping with treatment demands	25 (14/11)	63 (70/55)	The treatment demands or arising difficulties can be solved with the patient's own knowledge or skills so that they can deal with problems independently, develop strategies for overcoming them, or bring their own abilities for dealing with the demands.	“I tried, I repeated the exercises or changed my location so that the Wi-Fi connection was more stable and the exercise wouldn't cut off.” (P12)
		Support in case of difficulties	23 (13/10)	58 (65/50)	Support can be provided in dealing with the treatment demands or arising difficulties, e.g., the social environment, the therapist, or the technical support of the online platform can be contacted to solve problems.	“I would have written an email or asked my therapist.” (P8)
		Technical affinity	18 (7/11)	45 (35/55)	The patient's own technical affinity (i.e., knowledge or skills in dealing with technology), familiarity with technical devices, or sufficient technical knowledge is experienced as beneficial in dealing with the treatment demands.	“You definitely need to know how to handle phones or computers in general. (…) Just a bit of technical knowledge.” (P34)
	Barriers	Technical problems with OS	20 (10/10)	50 (50/50)	Patients report technical problems or errors in the OS that hinder access to or processing of the OS.	“Disturbing was that the technology often didn't run smoothly. So that things (…) were not sent or were interrupted.” (P23)
		Overload	17 (6/11)	43 (30/55)	Patients experience overload in terms of treatment requirements that are too difficult or exhausting. Patients report negative consequences due to excessive demands or difficulties due to challenging tasks or their own abilities (e.g., concentration).	“Overwhelmed, for example, when I don't understand something and don't know how to relate it to myself or what exactly it has to do with me.” (P17)
Optimization possibilities	Optimization possibilities for online sessions	Customizability of the OS in terms of lengths, content, and scope	13 (6/7)	33 (30/35)	Patients want the opportunity to deepen or expand the online content or to activate additional online content (e.g., further examples, additional materials) on request. Patients would like longer / more detailed or shorter / less detailed OS with increased or reduced time expenditure.	“Maybe they could have (…) incorporated an extension with more facts. An extension where you could challenge yourself a bit more if you wanted to. But something that isn't mandatory to read.” (P34)
	Optimization possibilities for the blending rhythm	More FtF sessions	23 (8/15)	58 (40/75)	Patients would like more FtF sessions overall or in relation to the OS (at a certain point in the therapy). Patients consider a larger proportion of FtF sessions and a smaller proportion of OS to be an optimal ratio.	“I would have preferred two-thirds of the sessions to be face-to-face sessions and one-third to be online sessions.” (P16)
		Regular blending rhythm	20 (15/5)	50 (75/25)	Patients prefer a regular blending rhythm or a blending rhythm according to a specific pattern.	“It's good to have therapy with the therapist in one week and then the online session in the next week. And then alternating again the week after. So, weekly alternation.” (P12)
		Balanced ratio of OS and FtF sessions	16 (11/5)	40 (55/25)	Patients consider a half-half ratio between FtF sessions and OS to be optimal.	“I would split it half-half.” (P6)
		Flexible blending rhythm	13 (3/10)	33 (15/50)	Patients prefer the possibility of organizing the number or sequence of OS and FtF sessions individually and flexibly according to their current needs. No regular blending rhythm is desired.	“Therapy sessions for me are optimal in a bi-weekly rhythm, and online therapy (…) is completely flexible, depending on whatever issue is acute for me at that time.” (P27)

Note. n = number of patients reporting a theme, % = percentage of patients reporting a theme, BT = blended therapy, OS = online session, FtF = face-to-face.

^a

Key theme = mentioned by at least 10 patients (25% of N = 40 interviewees).

Main findings

Patients reported more positive expectations than negative ones, aligning with previous research on BT acceptance. ¹⁹ Therapist behavior, specifically in encouraging participation, emerged as a crucial motivating factor, potentially influencing patient uptake of BT. Previous studies have shown therapists’ positive attitudes and high acceptance of BT^21,22,24 that might play a significant role in motivating their patients in BT. It is possible there is an interaction between therapists’ attitudes and patients’ own motivation and willingness to use BT, which are both highlighted as key facilitators from the blended therapists’ perspective. ²³

In line with previous findings, ⁴⁷ nearly all patients emphasized the importance of personal contact with the therapist during FTF sessions. This contact allowed individual and acute needs to be addressed and encouraged fostering of new perspectives, which were features not reported for online sessions. These findings align with patients’ frequent mentions of positive aspects of the therapeutic alliance, supporting previous research on a positive and strong working alliance in BT. ⁴⁸ Therapeutic guidance also emerged as a key facilitator for patient engagement and for integrating BT into the patients’ daily life, and support from others was a strong facilitator in enhancing the usability of BT. This result is consistent with other qualitative studies, which noted that connections with the therapist and supportive relationships motivated patients to persist with BT, ⁴⁹ and that the therapist was important in supporting patients’ use of the online platform. ⁵⁰ The importance of contact and support is further corroborated by quantitative research, which shows significant effects of guidance on the effectiveness and adherence of IMIs. ⁵¹ Therefore, compared to stand-alone IMIs or IMIs with low levels of guidance, the BT modality itself might be beneficial by including FTF contact with a therapist. Specific factors - especially therapist-related ones, such as the therapeutic alliance—can further facilitate or hinder engagement, as other previous findings indicate. ¹⁸ However, as our and previous research^18,23,29 shows, other factors, such as patient characteristics, perceived treatment outcomes, and treatment-specific features, should also be considered as facilitators and barriers. These factors might play a role not only in patient engagement but also in a successful implementation of BT in the other categories (fit, knowledge, usability, implementation) influencing treatment effects, as outlined in the Efficiency Model of Support. ⁴¹

In their expectations and experiences with online and FTF sessions patients noted distinct advantages and disadvantages. Our results suggest that time constraints in FTF sessions could be compensated by the highlighted location- and time-independent flexible use and the variable duration of the online sessions. The interviewed patients noticed actual specific benefits (e.g., FTF: personal contact, online: flexibility) and disadvantages (e.g., FTF: time constraints, online: no personal contact) of both BT elements, and not only expected these characteristics, as our findings on expectations and prior research have shown.^32,52 The respective advantages (e.g., of FTF sessions) seem to compensate for the limitations of the other element (e.g., of online sessions). This corresponds with previous work identifying patients as perceiving advantages and disadvantages of FTF and online elements as complementary. ⁵³

Moreover, across the interviewees’ statements on the characteristics of the two elements, it appears that some content is specifically suitable for each modality, like fictional patient examples and psychoeducation in the online sessions, or individualized topics in the FTF sessions. This aligns with insights from a Delphi study involving therapists and patients with varying experience in online therapy, which found that FTF and online elements were both considered appropriate for certain therapeutic content. ³⁰ However, content perceived as appropriate for both elements (cognitive techniques, practical exercises) possibly promotes reciprocal referencing between FTF and online sessions and the repetition and deepening of content. The results on online and FTF sessions characteristics from the interviewed patients’ perspectives imply that each seem to be essential core components of BT, with some content uniquely appropriate to each element, but may also serve supplementary functions and have overlapping content, as described in other studies. ¹⁸ A meta-analysis on BT by Nunes-Zlotkowski et al. (2024) suggested that supplementary BT (e.g., FTF as the main component and online sessions supplementary without new content, eight studies) may be more effective than designs with FTF and online sessions as integrated core elements (e.g., both elements indispensable, delivering unique therapeutic content, five studies). ¹⁸ In contrast, our findings show that the unique features of both elements are reflected as core components in the subjective change mechanisms, underscoring the importance of both FTF and online elements for the perceived BT's effectiveness in our interviewed participants.

Our findings on the implementation of the blending suggest that the combination of online and FTF elements has the potential to enrich treatment as most patients reported an active interplay between these elements, with reciprocal referencing or blending itself seen as a beneficial feature with positive treatment effects. Our results indicate that the online sessions are not merely conducted as a supplement to FTF therapy (or vice versa), but rather that a significant change of treatment, with integration and interaction between the two elements occur (e.g., incorporating online content into FTF sessions and blending activities of the therapist, like selecting suitable online sessions). This aligns with findings from a qualitative study, where therapists and patients noted that the integration of online elements positively transformed FTF therapy. ³³ The combination of the two elements allows for leveraging their respective benefits, and their interaction may result in additional advantages, such as more intensive treatment or further deepening of therapeutic content. However, preferences for the ratio of the elements varied. About half of the patients felt that FTF sessions were more important than online sessions, with more than half expressing a preference for having more FTF than online sessions. This preference was particularly expressed in the FLEX group, suggesting that the (regular) FTF contact with a therapist is an important element of BT, especially for patients receiving a flexible BT format. This could reflect a greater need for structure through the therapeutic guidance or the therapeutic contact as an important active component of BT. However, a conflicting finding of a meta-analysis indicates that a lower ratio of FTF sessions versus online sessions is associated with higher effect sizes. ¹⁸ Preferences of patients seem to be diverse, with some participants valuing both FTF and online sessions equally or favoring a balanced ratio in this interview study. Other studies found that most patients prefer an equal ratio or more online than FTF sessions, ³⁰ that actual BT session ratios vary between patients and primary and secondary care, ²⁰ and that therapists might favor more FTF sessions. ²³ Along with a range of optimization suggestions (each mentioned by only a few patients), our findings indicate that other factors might influence how BT should be implemented. Variables such as specific symptoms, the need for flexibility, socio-demographic characteristics, and individual skills and abilities—factors previously highlighted in research^23,31—may play a role in shaping preferences and the fit between patients and the treatment.

Overall, the main differences between the two BT versions, FIX and FLEX, primarily concerned themes closely related to the actual implementation of the versions, such as patients’ descriptions of the implemented blending rhythm and their preferences in this regard. Apart from these aspects, our findings indicated largely similar patient perceptions of the two versions, e.g., regarding treatment effects, characteristics of the treatment elements, facilitators, and barriers. Other factors may have been more influential in determining how patients perceived BT, such as how individual therapists implemented the assigned BT version. It is also possible that patient experiences were shaped more by shared characteristics of both versions, such as the use of online sessions per se, than by version-specific features. In existing BT formats, an alternating design (as implemented in the FIX group) is chosen more often than a case-to-case design (as implemented in the FLEX group). ¹⁸ However, our results show that patients emphasized advantages of both intervention groups, as the FIX condition might offer more structure, whereas the FLEX condition allows for adaptation of the blending rhythm to better suit individual needs. Patients’ preferences may be shaped based on their experiences with a specific implementation of BT. However, other factors might also play a role in preferentially choosing one of the two formats. For example, patient characteristics such as individual life circumstances and the need for flexibility, as well as therapist-related factors such as the therapists’ time capacities for offering FTF sessions (e.g., weekly, bi-weekly, or at irregular intervals) might be decisive. In this context, our results of comparing FIX and FLEX imply that the therapist may play a more important role in an alternating (FIX) design that may require more time capacities, while the time between FTF sessions (e.g., with exercises) might be more important in the FLEX blending rhythm.

Limitations

This study involves certain limitations. First, our sample was self-selected, limiting the representativeness of patients in the intervention groups of the PSYCHOnlineTHERAPY study. Nevertheless, all eligible patients at the time of this qualitative study were invited, achieving a high response rate of 49.4%. We excluded participants enrolled during the first months of the study due to technical problems with the online platform, as their inclusion might have biased the results. Patients who dropped out of BT before the interview invitation was sent (4.7%, n = 4/85) could not be included as they did not respond to the interview invitation. This may have resulted in an overrepresentation of favorable patient experiences in the data. However, some of the interviewed participants did report discontinuing online sessions during the interviews. While these participants were not formal dropouts, their experiences have provided insights into negative aspects and potential barriers regarding the engagement with the online sessions.

Second, we deviated from the study protocol by adopting a different theoretical model for the interview guide and deductive analysis approach. As outlined in the study protocol, ³⁴ the initial plan was to use the Unified Theory of Acceptance and Use of Technology model. ⁵⁴ Instead, we decided to choose the Efficiency Model of Support as the theoretical basis, as this model was particularly suited to the study of BT in its consideration of the interaction with a support figure (the on-site therapist in our case) and incorporation of multiple dimensions crucial for the implementation of BT.

Third, the final independent coding of the interview material yielded only weak to moderate inter-coder agreement. Despite extensive training, numerous consensus meetings, and the coders’ familiarity with the coding system, achieving higher agreement proved challenging. This was likely due to the large number of research questions, theme codes and detailed categories that were not further generalized to preserve essential information, the broad range of interview topics, or the different professional qualifications of the coders.

Fourth, we found that 30% of the patients in the FIX group did not receive the predefined alternating session rhythm of FTF and online sessions, limiting our possibility to compare these two BT formats. However, a considerably larger proportion of patients in the FIX, compared to the FLEX group received alternating FTF and online sessions, and there were also missing data as we had to rely on the therapist's session reports.

Fifth, due to the large number of 163 theme codes, only the main themes based on the predefined selection criterion are discussed in detail. An overview of all identified theme codes can be found in Additional file 4.

Lastly, data saturation remains uncertain, as some theme codes were mentioned by only one patient. This reflects the wide and diverse range of patient experiences but also shows that we might have obtained different results with more interviewees.

Implications and future research

We identified factors, such as fit and active components and mechanisms of change, that could serve as moderators or mediators in randomized controlled trials to determine who benefits from BT and which mechanisms drive treatment outcomes. ⁵⁵ As prior research shows,^20,23 personalization emerges as a key theme and reflects patients’ diverse preferences. Although research on outcome moderators in BT, as well as in IMIs ⁵⁶ and FTF treatments,^57–59 is still limited, therapists can tailor BT to the patients’ preferences, such as the need for flexibility or the desired BT version (FIX vs. FLEX) and ratio of online and FTF sessions. Existing recommendations on implementing BT, such as reviewing specific requirements (e.g., writing skills, motivation, internet access), can provide valuable insights. ³¹ Given that both BT versions were positively evaluated and largely comparable in terms of patient experiences, it seems warranted to pursue both formats in practice. Future research should further examine differential treatment effects of these BT versions to inform personalized treatment allocation and support the improvement of BT approaches. Our findings imply that important elements and advantages of FTF sessions (e.g., sufficient therapist contact and guidance) and online sessions (e.g., psychoeducation, symptom normalization by including fictional examples, stimulating self-management) should be given greater consideration in further development of BT and the practical application of the elements. Additionally, addressing negative expectations, adverse experiences, and perceived barriers also seem crucial. Although most participating patients did not report negative effects from BT, emotional distress due to online sessions and technical difficulties were commonly mentioned. Therefore, providing technical support and troubleshooting is essential to ensure the quality and further development of the offered BT. Potential negative effects of BT should be carefully investigated and managed with appropriate procedures, as these issues can also arise in stand-alone FTF treatments and IMIs.^60–62 Finally, comprehensive therapist training^23,29,50,63 is vital to ensure high-quality BT delivery, as the therapist, the therapeutic attitude towards BT, and the therapists’ BT implementation skills appear to be central components of successful BT.