Participants were selected through convenience sampling from a community sample of patients who had received a blended transdiagnostic group intervention for EDs at the Emotional Disorders Clinic of Universitat Jaume I [30]. Patients were required to be 18 years or older; no upper age limit was imposed. The initial sample included both individuals who had received psychological treatment prior to the feasibility trial and participants who were receiving psychological therapy for the first time.

Patients began the same intervention but differed in their level of treatment adherence; 23 out of 34 participants (68%) completed the full intervention, and 11 out of 34 (32%) discontinued treatment [30]. Therefore, this study included 2 subsamples based on treatment completion status. This was done to explore the experiences of those who finished the intervention and those who dropped out.

The first subsample consisted of 18 patients (14 women and 4 men) who completed the full intervention protocol, with a mean age of 33.94 (SD 11.03; range 20‐54) years. Sociodemographic and clinical characteristics of participants at the beginning of the treatment can be found in Table 1.

The second subsample consisted of 4 patients (all women) who initiated but discontinued the intervention before completing it (dropout). Their mean age was 28.5 (SD 12.39; range 21‐47) years. Sociodemographic and clinical characteristics of these participants at the beginning of the intervention can be found in Table 2.

The treatment in which all participants previously took part was a transdiagnostic CBT intervention designed to address ED, composed of 16 modules and lasting 24 weeks. It was delivered in a group and blended format, so that patients attended a total of 8 group sessions by videoconference (2 hours in duration), and, in the period between sessions (3 weeks), they worked on the therapeutic content through online modules on a web platform. In this platform, the recommendation was to advance at a rate of approximately one module per week, allowing participants to consolidate therapeutic content between sessions. During the intervention, 2 messages of support per week were sent to participants (an email and an SMS text messaging). These messages served as reminders and motivational prompts to encourage continued participation. Further details regarding the intervention structure and content can be found in the study protocol [23] and in the paper on quantitative results [30].

The qualitative data collection procedures differed according to participants’ treatment completion status. On the one hand, those who completed the treatment (n=23) were invited to participate in focus groups (in-depth group opinion interviews). This was done with the goal that interview participants had sufficient knowledge about the intervention and could provide more complete opinions on all the aspects explored. Invitations were made during the final treatment sessions and by email. Finally, a total of 18 participants accepted and took part in the interviews (subsample 1), while the remaining 5 were unable to attend.

A total of 4 focus groups were conducted, one per treatment group, each lasting approximately one hour. Meetings were held via videoconference between 2 and 5 weeks after the end of treatment. All interviews were recorded and subsequently transcribed verbatim for later analysis. No field notes were taken.

Each focus group was conducted by 2 psychologists from the research team. In total, 5 psychologists (4 women and one man) conducted the interviews; 3 of them PhD students (NJ-O, Macarena Paredes-Mealla, and Rosa Lorente-Català) and 2 were PhDs in psychology with previous experience in qualitative research (AD-G and Alberto González-Robles). All interviewers were also experienced clinicians and researchers in transdiagnostic and internet-based interventions. These psychologists were the therapists for the therapy groups in the feasibility study, so to ensure an unbiased procedure, they only interviewed those participants who had not previously been their patients (eg, Macarena Paredes-Mealla and Alberto González-Robles moderated an interview with participants whose therapy group had been led by AD-G and NJ-O). During the focus groups, there were no observers; only the 2 interviewers and the participants were present. Participants were informed that the aim of the study was to explore their opinions and experiences in order to improve the future implementation of the intervention.

Focus groups continued until all available participants from the previous study had been interviewed, corresponding to one group interview per therapy group. The research team determined that data saturation had been reached. According to Krueger and Casey [31], a commonly accepted rule of thumb is to plan 3 or 4 focus groups for a specific audience and, once they have been conducted, determine whether data saturation has been reached, that is, the point at which ideas begin to be repeated and no new information emerges. Furthermore, in the consensus qualitative research (CQR) methodology, it is recommended to include at least 8‐15 participants to achieve data saturation [32,33].

On the other hand, participants who did not complete treatment (n=11) were invited via email to complete a brief open-ended online questionnaire aimed at exploring their reasons for dropping out. A total of 4 participants completed this questionnaire (subsample 2), while the remaining participants did not respond to the questionnaire nor to the email.

Following recommendations [31,33], a semistructured interview with 12 open-ended questions was developed to explore participants’ perceptions and experiences in depth through focus group discussions. To that end, 2 doctoral students reviewed the literature of qualitative studies on psychological interventions, including those using blended treatment formats. Afterward, each doctoral student independently designed a list of relevant interview questions, which were then shared and discussed collaboratively until consensus was reached. Finally, 2 senior researchers (AD-G; JB-L) and full professors reviewed the proposal of questions, and the final version was defined. An effort was made to reach a balance between obtaining the greatest amount of information possible and asking the fewest number of questions. The interview script can be found in Multimedia Appendix 1. Two questions that constituted the dropout questionnaire can be seen below in Table 3.

The CQR methodology [32,33], which is a structured and rigorous method for analyzing qualitative information, was used to analyze the focus group data. This methodology combines elements from constructionism and from postpositivism, and seeks to understand people’s subjective reality while simultaneously reporting that reality as objectively as possible [33].

Two doctoral students trained in qualitative analysis acted as judges (NJ-O and AF-J), and 2 full professors with prior experience in qualitative research acted as auditors (AD-G and JB-L). All researchers involved in the analysis were women. One of the judges also served as an interviewer in the study.

First, the 2 judges independently identified the domains and then pooled them until a consensus was reached. The 2 auditors reviewed the proposed domains and again a consensus was reached between all of them. Subsequently, the judges independently identified and placed the core ideas from each interview into the corresponding domains and then shared them until a consensus was reached. Core ideas were also shared interview by interview with the auditors, and the necessary modifications were made until consensus was reached again. Finally, cross-analysis was carried out and the categories were established, following the same consensus procedure explained above. The information has been identified from the data (data-driven coding), although the domains partially correspond to the interview questions.

Following the suggestions of Hill et al [33], the frequency of each category was quantified to indicate its representativeness. Categories were labeled as “General” if they applied to all or all but one case (17‐18 cases), as “Typical” if they applied to more than half of the cases (10‐16 cases), as “Variant” if they applied to half or fewer of the cases (3‐9 cases), and as “Rare” if they applied to only 1 or 2 cases.

The information available regarding the reasons for the dropping out of the participants who discontinued the intervention was very limited, so it was not considered appropriate to conduct a formal qualitative analysis based on an established methodology. Instead, this information was treated descriptively as complementary to the insights gathered in the focus groups. Nonetheless, the key themes identified independently by the 2 judges are briefly reported.

The COREQ (Consolidated Criteria for Reporting Qualitative Research; Checklist 1) [34] guideline was used to report the results.

The study received approval from the Ethics Committee of Universitat Jaume I (CD/40/2019) and all participants provided informed consent prior to participation. Participant data were handled in accordance with applicable data protection regulations. Privacy and confidentiality were ensured by anonymizing all data and storing them securely on password-protected institutional servers accessible only to the research team. No personally identifiable information is reported in the manuscript. Participants did not receive financial compensation for their participation in the study.

A total of 8 domains and 47 categories were identified after analysis using the CQR method, 10 of which were categorized as “Typical,” 31 as “Variant,” and 6 as “Rare.” The results obtained from the focus group interviews are shown in Table 4, which includes several illustrative core ideas according to the frequency of the category.

This domain includes all aspects related to the structure of the blended intervention and how its different components were combined or organized.

This section includes all the experiences and opinions regarding the treatment modules or therapeutic strategies, which were taught both in the group sessions and on the online platform. The categories found are described and exemplified below.

All experiences and opinions related to group sessions by videoconference are included here. Aspects related to the frequency and/or duration of the sessions, already included in the configuration domain, are not included in this section.

This domain encompasses all the experiences, assessments, and opinions regarding the role of the therapists in the intervention, including therapeutic support received, therapeutic alliance, etc. The identified categories are outlined and illustrated below.

This section includes all experiences, opinions, and assessments regarding the intervention as a whole, including its impact or effects, its advantages and disadvantages, etc.

This domain includes participants’ opinions and experiences regarding the aspects of the intervention that helped them to stay motivated, continue progressing with the treatment, and promoting adherence to it.

This domain refers to any suggestion, proposal, or idea to improve the intervention in any way from the patients’ point of view.

Participants suggested some modifications to the platform, aimed at improving the current functionality or incorporating new tools. We can see an example in the following extract:

Participants proposed some adjustments regarding the pace of progress on the platform and the duration and periodicity of sessions, as exemplified below:

Some participants made suggestions about the sessions, proposing some additional sessions or that some of the sessions be held in person.

Participants who discontinued the intervention identified various reasons for dropping out. Participants mentioned treatment-related variables (lack of results, treatment-related stress, or difficulties applying the strategies), person-related variables (low involvement, lack of motivation and energy, or time constraints), and the need for other types of help (in-person or more specialized professional help). As strategies to improve adherence to the treatment, participants suggested adjustments in the format and configuration of the sessions (individual and in-person or weekly) and other aspects (less homework tasks and more time to discuss individual problems). Table 3 shows the literal responses to the dropout questionnaire.

The goal of this study was to explore in depth the experiences and opinions of patients who received a transdiagnostic CBT intervention for ED, delivered in a blended and group format, in order to understand their degree of acceptance and improve the future implementation of these types of interventions.

Overall, the results of this study indicate a general satisfaction with the transdiagnostic intervention, consistent with prior evidence on the feasibility and utility of blended psychological treatments [26,35]. Positive perceptions were observed across multiple dimensions, including the usability of the web platform, the perceived richness and relevance of the therapeutic contents, the added value of group format, and the perceived support provided by the therapists. Furthermore, participants generally reported perceived improvements following the intervention and emphasized the advantages of this blended format. Consequently, this intervention appears to be both feasible and well-accepted by patients for the treatment of ED. The results of this study also provide relevant information on specific measures that could be adopted in the future to further optimize treatment and minimize dropout rates.

Generally, participants reported an overall positive user experience with the platform, particularly regarding its intuitive design and the availability of multimedia materials and contents. They also appreciated the different tools offered by the platform. These results are consistent with the previous feasibility and acceptability study in which the patients included in this study participated [30]. In the aforementioned study, adequate adherence to the platform and high-excellent usability according to the System Usability Scale [36,37] scores were observed. Previous studies on other treatment protocols administered through the same web platform also reported high usability scores [38,39]. In addition, these findings align with research suggesting that ease of use, clarity, usability, attractive appearance, and perceived utility are critical factors in the acceptance and engagement with digital mental health interventions [40,41]. Participants also identified some technical difficulties with the platform, such as progress within each module not being saved and disconnection of the platform after a period of inactivity that required them to log in again. However, this feature was intentionally implemented as a security measure to protect users’ privacy if the platform was accidentally left open. A future challenge will be to maintain robust security standards that enable patients to use digital devices confidently and safely [42] without compromising usability and acceptability. Technical problems have also been reported in other studies of blended interventions [12,26,27], suggesting that the difficulties identified in this study are common in this field.

The mixed evaluations of pace of progress on the platform reflect a common challenge in online and group interventions: balancing standardization with individualization. While participants were generally satisfied and considered the weekly pace adequate, others wished for a more flexible rhythm, particularly for modules involving complex skills such as emotional avoidance or acceptance. Prior literature suggests that personalizing the configuration of blended treatments may enhance adherence and treatment benefits [43]. As the systematic review by Erbe [14] indicates, there is no single optimal ratio between face-to-face and online components in blended interventions; thus, patient-specific customization may be key. The length of the sessions was considered appropriate by most participants in focus groups, although a few felt they were slightly long. There were also differing opinions on session frequency; some found the timing adequate to work on the content of the modules, while others would have preferred more frequent sessions or less time between them. These findings are in line with the heterogeneity of session lengths reported in the literature. For example, Osma et al [44] implemented 2-hour unified protocol group sessions, while Schuster et al [45] noted that therapists were concerned that 90-minute weekly sessions did not allow enough time for discussion. This variability of configurations in the literature highlights the need to customize the specific combination of in-person and online elements, as well as the timing. This personalization of the intervention has been emphasized by Fernández-Álvarez et al [12] and Patel et al [13], especially within transdiagnostic frameworks where symptom profiles and levels of functional impairment can vary significantly. Although not asked directly, a couple of focus group participants talked about the duration of the treatment. While one participant felt that the duration had allowed them to track progress month by month, another participant believed that it could cause a loss of motivation. Interestingly, participants mentioned personal variables that had an impact on the optimal fit of the planned configuration. These insights suggest that individual factors, such as workload, time management challenges, or fluctuating symptoms, may impact the optimal engagement and highlight the value of adapting to the patient’s life circumstances.

Participants highlighted the appropriateness and richness of the content. They valued the material positively, indicating that it is a very comprehensive program and suggesting that everyone should have access to the modules. They stated that the content was well explained and relevant to their issues. They also pointed out which content had been most useful for their specific cases. Mindfulness was the strategy mentioned by more participants, followed by activities belonging to the positive affect component—such as value-based behavioral activation or the identification of psychological strengths—and emotional avoidance and emotion-driven behavior modules. It may be thought that patients could be reluctant to adopt strategies like mindfulness, as avoidance is a common trait among people with ED [46]. Therefore, it is very important to note that participants responded positively to mindfulness and felt it was very helpful, as it was the strategy most frequently mentioned. They also highlighted the exposure component, cognitive flexibility, and relapse prevention as other useful strategies, providing a comprehensive overview of the entire program. Overall, these results align with previous quantitative findings. When participants were asked how useful each module was on a scale from 0 to 10, the average scores were 7 or higher for all modules [30]. Another important point from participants’ feedback was the variability in prior knowledge and its impact during treatment. Some participants felt unsure about which strategies to use in specific situations, while others sometimes found the content repetitive due to their previous familiarity with similar material. Previous research emphasizes the need to tailor the complexity of therapeutic content to participants’ prior knowledge and learning styles [47,48]. These findings suggest the value of preassessment tools to gauge prior familiarity with CBT concepts, which could help guide each patient’s pacing or personalized use of modular content.

Regarding the group format, participants noted some limitations and expressed initial reluctance toward this approach. However, most participants recognized positive aspects, such as learning from others and feeling a bond with the group. This aligns with literature highlighting the therapeutic value of shared experiences, group cohesiveness, and peer learning among individuals with similar issues [20,49,50]. Numerous studies on the acceptability of transdiagnostic interventions report good acceptance and high treatment satisfaction, and this is held in a group setting [51,52]. In terms of videoconferencing, participants identified limitations like potential connection issues and challenges in finding a private space. However, they also highlighted several advantages, such as the convenience of joining sessions from anywhere and the fact that emotions surfaced in the same way through videoconferencing as in face-to-face therapy. These benefits and additional advantages of this form of psychotherapy have been noted in previous literature [49,53]. This research indicates that, in general, patients have a positive attitude toward videoconferencing as a therapy option [54-56]. In line with this, some participants in this study reported satisfaction with the sessions and positively valued the dynamics of group interactions. However, despite these benefits, some participants expressed a personal preference for individual or in-person therapy. This preference was one of the recruitment challenges faced in the treatment feasibility study [30]. Previous literature has also reported that some individuals prefer in-person groups [49], and many patients with ED often favor individual face-to-face therapy [57]. Therefore, it is crucial to explore ways to make more acceptable those interventions that enhance the cost-benefit balance.

Most participants highlighted the qualities of the therapists and their availability, such as their explanations, their empathy and closeness, their expressiveness, or their response to doubts that arose, among other issues. Additionally, in general, participants emphasized the importance of the therapist’s role, indicating that it was fundamental and that without therapists they could not have done it. Likewise, they reported having established a good alliance with the therapists in the same way as in classical psychotherapy. This is consistent with previous studies in which the importance of support from therapists was highlighted [12,13]. The establishment of a strong therapeutic alliance, even in an online group format, was reported by several participants, consistent with previous research demonstrating the feasibility of alliance building in digital contexts [58]. Furthermore, research shows that patients and therapists experience a good therapeutic alliance with videoconferencing therapy, comparable to that obtained with face-to-face therapy [55,59-61]. Studies on blended interventions also show that it is possible to establish a good therapeutic alliance between therapists and patients in this format [26,35].

Participants identified several general advantages of the blended intervention they received, notably temporal flexibility and, particularly, spatial flexibility, which allows treatment to be accessed from anywhere without the need to travel. Additionally, the combination of online modules and sessions was highlighted as a positive aspect, with both elements considered useful. These advantages have been noted in other studies of blended interventions. For instance, in the study by Etzelmueller et al [26], patients also emphasized the spatial flexibility and convenience of working from home, and they found the combination of online modules and synchronous video-based sessions to be beneficial. The main disadvantage identified by participants in focus groups was the more general nature of the treatment, which limits in-depth exploration of individual circumstances or specifics. This is related to the transdiagnostic nature of the intervention and likely its group format. Despite this, most participants reported perceived improvements and the usefulness of the skills learned in their daily lives, noting that they have discovered methods that work for them, that they can better cope with difficult situations or their own symptoms, or that they feel better overall. This is consistent with the preliminary efficacy found in our previous study [30], where significant reductions in anxious and depressive symptoms were obtained at posttreatment and follow-up compared to baseline, and where significant changes were found in other clinical measures, such as negative affect, neuroticism, emotion regulation, or quality of life. In other blended interventions mentioned above [26], patients also reported positive treatment effects. Focus group participants also expressed satisfaction with the intervention, and some even said they would recommend the treatment to others with ED. This is consistent with the quantitative satisfaction reported in our previous study, where patients showed high satisfaction with the treatment [30]. It is also in line with previous research, which generally shows positive opinions [26,27] and high satisfaction with blended interventions [16].

Regarding the domain related to elements that helped them maintain adherence, the most frequent category was therapeutic support, which once again highlights the importance of the therapist’s presence. The existence of scheduled sessions and the commitment to groupmates were mentioned, which also appears to reinforce the importance of support and guidance from therapists as well as one of the advantages of the group format [20,21]. Other important points were the therapeutic materials themselves and the effects of the treatment on the patients, both in terms of their personal experience of improvement and the possibility to see their progress reflected in the platform’s graphs. In addition, although less frequently mentioned, some participants described internal factors, such as readiness to change and self-commitment, pointing to the role of intrinsic motivation. Taken together, these findings suggest that successful adherence in blended formats likely results from a combination of external (therapist, structure, characteristics, and content of treatment) and internal resources (motivation and self-management), supporting recent models of digital intervention engagement [62]. Future adaptations might benefit from integrating dynamic feedback systems and tailored support strategies to further optimize adherence.

With regard to this, during focus groups, participants suggested incorporating some changes to the platform, such as a discussion forum or a greater degree of interactivity. They also proposed adapting the configuration to the specific modules to be worked on or making the sessions more frequent, or even some of them in person. In addition, they proposed a greater individualization of the intervention, suggesting creating brief individual spaces with the therapist or combining some individual sessions with the current intervention. They also made proposals to improve adherence to treatment, some of which were also related to more individualized follow-up or leaving less space between sessions. Thus, the importance for patients of the presence of the therapists throughout the intervention and the customization of treatment is once again evident.

Finally, participants who dropped out of treatment provided reasons for dropping out and suggested some strategies to improve treatment adherence. Although they did not complete the program, we considered it important to include their experiences to enrich understanding of the intervention’s acceptability and identify potential barriers to engagement. Similar to what was found in previous studies [12], participants mentioned that the treatment was not working for them, that they had difficulty applying the strategies learned, or that they identified the need for other types of assistance, such as in-person or more specialized help. The relevance of addressing these aspects has been previously evidenced because noncompletion of tasks generates dissonance, may lead to increased discouragement, and is related to treatment success [27]. Dropout participants proposed changes regarding the format and configuration of the sessions with the aim of improving adherence to treatment, suggesting that they could be individual, in-person, or held weekly. They also believed that having more time to discuss individual problems in sessions or having fewer homework assignments could help to increase adherence. It has been shown that patients who engage more with homework assignments in online CBT interventions achieve a greater reduction in anxiety and depression symptoms [63], so it would be important to assess patients’ engagement in this regard to be able to implement preventive strategies. Several of the identified barriers and proposed suggestions for improvement coincide with aspects mentioned by participants in the focus groups, which reinforces the value of the findings obtained. Taken together, the importance of focusing on the personalization of treatment emerges.

Although this format may not be suitable for all individuals, the findings from the feasibility study [30], together with the qualitative results from this study, support the viability and acceptability of this blended intervention, which also appears to have clinical utility. Additionally, it may help to overcome some of the disadvantages of fully face-to-face and fully self-administered formats and may be a good resource to facilitate access to EBT for a broader population. This is particularly relevant in the context of public health systems such as the Spanish NHS, where there are long waiting lists and sessions occur infrequently. Therefore, a key recommendation for future research and clinical practice would be to explore which patient profiles and under what circumstances this type of blended intervention is most effective [43], as well as to identify cases where alternative formats may be more beneficial.

This study has several limitations. One of them is that retrospective responses pose a methodological limitation due to possible recall bias. However, this is a common limitation in qualitative research and not specific to this study. Nonetheless, the focus groups were conducted shortly after the end of the intervention, which likely reduced the extent of this bias. An additional limitation is that 2 of the participants in the focus groups hardly spoke during the interview, resulting in very few ideas from them, which made it difficult to reach the “General” category. Another limitation is that very few participants who dropped out of treatment completed the dropout questionnaire, so formal qualitative analyses could not be conducted. Finally, it would be advisable for future studies to be conducted with people treated in other settings, such as the Spanish NHS, in order to increase the generalizability of the results.

Despite the aforementioned limitations, this study contributes to completing the established conclusions regarding the feasibility, acceptability, and preliminary efficacy of the intervention studied [30]. Furthermore, to our knowledge, it is the first qualitative study to explore the opinions of patients (completers and noncompleters) who have received a transdiagnostic intervention applied in group and blended formats, thus contributing to the development of this novel format.

This study reinforces the feasibility and acceptability of a blended transdiagnostic group treatment for ED. These qualitative findings provide valuable insight into patient experiences, perceived benefits, and areas for improvement while also offering guidance for future research and implementation. This study supports this innovative format as a potentially scalable, acceptable, and effective option within mental health services.