Summary of main findings

Therapists overall rated most components higher than service users, with only four items being excluded and four items being re-rated at Round 2, compared with 13 exclusions and 15 items being re-rated by the EbE group. There was disparity in perceived importance of numerous components between the groups.

Behavioural activation is a component considered to be a well-established part of the treatment of depression (Mazzucchelli et al., Reference Mazzucchelli, Kane and Rees2009) and has demonstrated efficacy (Parikh et al., Reference Parikh, Quilty, Ravitz, Rosenbluth, Pavlova, Grigoriadis, Velyvis, Kennedy, Lam, MacQueen, Milev, Ravindran and Uher2016). The aim of behavioural activation is to increase user engagement in positively reinforcing activities, with the initial behavioural model being based upon the assumptions that low levels of response-contingent positive reinforcement can contribute to and maintain depression (Dimidjian et al., Reference Dimidjian, Barrera, Martell, Muñoz and Lewinsohn2011). While therapists considered this component important, EbEs did not. The clinical utility, importance, and acceptability of behavioural activation have been confirmed in various studies (Simmonds-Buckley et al., Reference Simmonds-Buckley, Kellett and Waller2019). This could suggest that a clearer rationale for its purpose and effectiveness could be needed at the start of therapy in order to support engagement. However, it is possible that this result is due to the nature of the strategy itself, designed to put the client into situations they may feel unable to engage with naturalistically. Stressful components such as behavioural activation can result in departures from treatment plans, due to either the client’s negative feelings towards the component or from the clinician in the form of therapist drift (Waller, Reference Waller2009). Findings such as this raise important discussions about the difference between outcome and acceptability, weighing the applied real-life value of components that have established clinical efficacy, but may have lower acceptability with users.

Homework was another component that reached consensus in therapist panel but did not in the EbE panel. Homework has been found to be a useful component of CBT, with homework compliance found to be a positive predictor of therapy outcome, and homework assignments producing significant positive effects on therapeutic outcomes (Kazantzis et al., Reference Kazantzis, Lampropoulos and Deane2005). However, Helbig and Fehm (Reference Helbig and Fehm2004) described problems with homework in CBT as ‘rather the rule than the exception’ (p. 298), with therapists reporting problems relating to user completion and compliance in more than 50% of cases, most frequently with users doubting their ability to manage the task and worrying about the difficulty. CBT can be perceived by users to be difficult and demanding (Yarwood et al., Reference Yarwood, Taylor and Angelakis2023). For many, particularly those experiencing more severe difficulties, or for those with limited energy or time due to many factors such as disability, work, or family responsibilities, homework tasks may be challenging to adhere to. Given how useful this component is to therapeutic outcomes, it is important to consider the reasons why recipients may feel unable to regularly complete homework tasks, or may feel homework is unhelpful or unpleasant to them.

There was further disparity with components that ≥80% of therapists rated as important, but did not reach consensus threshold for EbEs. These included: using measures to determine severity of depression and to monitor improvement, exposure tasks, providing documents/worksheets, behavioural experiments, and psychological formulation. The most significant disparity in therapist and EbE rating was behavioural experiments at 97.2% and 50%, respectively. Although they are primarily utilised in the treatment of anxiety disorders, there is some evidence to support the usefulness for behavioural experiments in the treatment of depression (Skilbeck et al., Reference Skilbeck, Spanton and Roylance2020).

Inversely, there were differences that EbEs found important, but therapists did not. Session summaries, for example, help to ensure that key components of the session have been highlighted and understood (Sadeh-Sharvit et al., Reference Sadeh-Sharvit, Rego, Jefroykin, Peretz and Kupershmidt2022), but interestingly their provision was not deemed important by therapists in this sample. This may be due to therapists’ belief of its unimportance, or perhaps its impact is believed to be relatively low when viewed within the context of the additional time needed for clinicians to provide for each client. Remaining differences in perceived importance included: CBT following a recognised protocol, sessions being delivered face-to-face online or in person, and sessions lasting 50–60 minutes. These components are notably all in the hands of the clinician or wider health service, and are not often an option that a recipient can advocate for themselves and their needs. This perhaps speaks to a lack of choice and agency available to therapy users, and consideration of their inclusion could be an important factor in engagement and acceptability. A clear first step for future research is therefore to understand the basis of these differences by establishing why EbEs find certain elements to be more or less important. Qualitative interview studies with those who have received CBT would provide further insights here. Following this, research should establish whether these differences are based on factors such as knowledge, perceived ability to complete certain components or perceptions about therapeutic benefits and whether targeted psychoeducation impacts on EbE views.

There were multiple items which both EbEs and therapists agreed upon; notably, items relating to the content component of cognitive restructuring. This term refers to the collection of strategies aiming to support recipients in identifying, evaluating, and modifying maladaptive thoughts and beliefs (Wenzel, 2017). These strategies are emphasised as a core element in the treatment of many mental health difficulties such as depression, and when utilised in CBT are typically integrated with behavioural methods (Ezawa and Hollon, Reference Ezawa and Hollon2023). However, in this study, receivers of CBT placed less emphasis on importance of behavioural strategies, showing preference towards cognitive components.

All items categorised as clinician factors achieved consensus in both groups. Several of the most highly rated components by both therapists and EbEs related to clinician traits: being trustworthy, understanding, and non-judgemental were rated as important by 100% of participants in both sample groups. These findings mirror evidence from previous research. The synthesising of qualitative data of CBT experiences has found that positive therapist traits and their role in the development and maintenance of the therapeutic alliance were important factors in therapeutic recovery (Yarwood et al., Reference Yarwood, Taylor and Angelakis2024). Therapist knowledge was also rated at 100% by both therapists and EbEs. While this finding might be somewhat unsurprising, establishing the level of consensus systematically was important. Furthermore, findings highlight the relative importance of therapist qualities, as EbEs rated these items higher than any others, including items relating to therapeutic content. The overall consensus ratings highlight the high level of perceived importance of the clinician as a therapeutic factor of CBT.

Mindfulness did not reach consensus for EbEs or therapists; it was the lowest rated component for therapists, and the third lowest rated component for EbEs. While mindfulness is traditionally a feature of third wave therapies, it has become a common feature of therapeutic practice (Arthington, Reference Arthington2016). While there are no data to support direct reasoning for this, two possibilities for this agreed lack of importance may firstly be the belief that it is not a traditional feature of second-wave CBT, or perhaps a belief in its inefficacy in the treatment of depression. There is much research supporting the efficacy of mindfulness in the treatment of depression (Hofmann et al., Reference Hofmann, Sawyer, Witt and Oh2010; McCarney et al., Reference McCarney, Schulz and Grey2012); however, both therapy recipients and therapists in our study did not reach a consensus on its importance. One reason for this might be that mindfulness techniques often take time to learn, appreciate, or to incorporate into regular practice, even if the exercises themselves are short in duration. Mindfulness is often misperceived as a simple technique, which belies both the skills and complexity needed to benefit from mindfulness (Russell and Siegmund, Reference Russell and Siegmund2016). In short-term therapies, there may simply not be enough time to properly introduce, practise, and integrate mindfulness into the process. As a result, both therapists and clients might view mindfulness as less impactful when the therapy is so brief. England’s Talking Therapies service provided on average only 8.3 sessions for CBT in 2022–2023 (NHS England, Reference NHS2024), leaving little time for mindfulness. However, more research is needed to explore these hypotheses, and would benefit from additional qualitative inquiry in order to better understand context and experiences behind the quantitative data.

Comparison with similar research on treatment components

A randomised optimisation trial based on 767 adults with depressive symptoms found no significant differences among six groups of participants receiving different components of internet-delivered CBT for depression at both post-treatment and 6-month follow-up (Watkins et al., Reference Watkins, Newbold, Tester-Jones and Collins2023). The only active CBT component that showed a small but significant reduction in depression at 6 months was absorption training, which focuses on enhancing engagement with activities. This was the first large-scale study to examine the effectiveness of CBT components that were delivered online using a factorial design. Furthermore, the study’s findings suggested that internet-delivered CBT could be as effective as traditional CBT.

Complementing these findings, a network meta-analysis (Angelakis et al., Reference Angelakis, Huggett, Gooding, Panagioti and Hodkinson2022) compared core, complex, and ultra-complex CBT protocols, demonstrating that while all treatments were effective in reducing depression post-treatment, only complex and ultra-complex protocols, incorporating additional components to cognitive restructuring and behavioural activation, maintained their benefits beyond 26 weeks. Ultra-complex CBT, which was based on at least four different therapeutic components, was particularly beneficial for individuals with co-morbid conditions and those from lower socioeconomic backgrounds, and its benefits persisted over time.

Our findings, examining both therapist and expert by experience perspectives on CBT, also highlighted the importance of therapists’ qualities, such as being knowledgeable and trustworthy. A notable difference between our findings and those of Watkins et al. (Reference Watkins, Newbold, Tester-Jones and Collins2023) was that, although absorption training was found to be the only significant treatment component (sharing similarities with mindfulness, as both focus on engagement in specific tasks occurring in the present moment), mindfulness in our study was judged as less important by both therapists and experts by experience. This is an interesting finding, and more research is needed to determine whether absorption training and mindfulness could be both important and acceptable therapeutic components, in addition to being effective in treating depression.

When juxtaposed with our study’s findings, the Angelakis et al. (Reference Angelakis, Huggett, Gooding, Panagioti and Hodkinson2022) results emphasised an important distinction: while therapists prioritised established core components like behavioural activation, recipient perspectives from our study indicated that these elements may not be viewed as essential. This raises questions about whether traditional CBT components, such as homework and behavioural activation, are always the most impactful or whether their effectiveness is context-dependent, particularly for recipients with varying levels of engagement or specific socioeconomic challenges. Furthermore, the findings from Angelakis et al. (Reference Angelakis, Huggett, Gooding, Panagioti and Hodkinson2022) reinforce the importance of broadening CBT frameworks to include more diverse and context-sensitive therapeutic components, ultimately improving the acceptability and long-term efficacy of CBT interventions.

Strengths and weaknesses

The Delphi method itself typically utilises professional experts in seeking to gain a consensus. This research is important in that it contributes to a comparatively small existing literature pool of Delphi studies which value the perspective and knowledge of individuals with lived experience of the topic such as Law and Morrison’s (Reference Law and Morrison2014) recovery in psychosis study, and Ropaj et al.’s (Reference Ropaj, Haddock and Pratt2023) recovery from suicidal ideations study. Furthermore, this study is one of very few to deviate from the traditional utilisation of the method in order to obtain one consensus, but rather views the findings comparatively in order to better understand the perspectives of people with lived experience against those of professional experts. This includes Richards et al. (Reference Richards, Woolrych, Allen and Schmidt2022) who compared the perspectives of people with lived experience of eating disorders and clinicians on priorities for eating disorder services, and Krysinska et al. (Reference Krysinska, Ozols, Ross, Andriessen, Banfield, McGrath, Edwards, Hawgood, Kõlves, Ross and Pirkis2023) who explored best practice for involvement of people with lived experience of suicide in suicide research, including both suicide researchers and individuals who themselves had lived experience of suicide.

The first weakness to consider is inherent to the Delphi approach itself. While the method has clear value, there is no one standardised way to measure consensus, and it has been criticised as being unscientific (Yousuf, Reference Yousuf2007). This is displayed through the literature through varying percentage cut-offs and analysis methods, with almost no single modified Delphi being conducted the same way (Shang, Reference Shang2023). Analysis and consensus measurement for this study were carefully considered based upon multiple factors including the nature of the topic, previous published literature, and PPI contributions. While there are methodological issues with the Delphi method as a whole, the process has inherent value. The Delphi method is a format that enables anonymity, creativity and honesty, which can contribute to the understanding and resolution of problems (Fink-Hafner et al., Reference Fink-Hafner, Dagen, Doušak, Novak and Hafner-Fink2019). Similarly, there is no encompassing definition of the essential components of CBT for depression. Efforts were made to capture a comprehensive range of key depression-focused CBT practices while keeping the item list minimal in order to reduce participant fatigue and time burden. However, in doing so, this may have resulted in components that may be important being omitted from the list. This was accounted for by providing both groups of participants an open text response to suggest missing components, although none were identified this way.

The study would be strengthened with more detailed characteristics of therapist practice including time as a therapist and how many clients with depression they have treated, as well as additional EbE information pertaining to the length and nature of the intervention received. The therapist sample may skew towards those who work within private practice due to the amount of recruitment from independent therapists who listed their practice publicly. As it was not possible to determine the exact reach or representativeness of recruitment for either the therapists or the EbEs, this is a potential source of bias. Selection bias was reduced through a lack of incentives to take part, with all respondents in both panels being volunteers who were not renumerated for their participation. A suggested area of future research would be to explore the similarities and differences in perceived importance of therapeutic components in those working within private and public health settings; additionally, examination of the difference between those self-funding CBT and those receiving National Health Service (NHS) delivered therapy. The difference between the UK’s public health delivery and other countries may also make these results less generalisable to other countries for which CBT is prescribed differently.

Related to this is the fact that EbEs themselves could have had diverse experiences of CBT. For practical reasons connected to recruitment, details of participants’ own experiences were not gathered. While participants were asked to focus on their perspective as either a deliverer or recipient to account for those who may have met the inclusion criteria for both samples, the dual ‘patient–therapist’ identity may be difficult to separate. Future Delphi studies could include this type of information, and other forms of research such as qualitative interviews would be ideal to explore this in depth.

The findings of the study leave room for interpretation. While participants were asked to rate items by importance based on their personal beliefs and experiences, importance can mean different things to different people. A lack of agreement on importance does not in and of itself mean a component is unacceptable, nor does an opinion on importance tell us how well a component was understood. The use of participants selecting ‘unsure/do not know’ on several questions made interpretation of the analysis on those items difficult, particularly responses from EbEs. This could be attributed to participants being unsure about or having mixed feelings about the component (such as ‘I hated doing it, but it helped me’, for example), or being unfamiliar with an item due to lack of inclusion in their own intervention. Understanding of CBT components and terminology was supported through the inclusion of a plain-English glossary of terms (Appendix B in the Supplementary material). Additionally, items with therapeutic terminology such as CBT following a recognised protocol, relapse prevention, clinical supervision, and therapeutic alliance met consensus when rated by EbEs, indicating a strong understanding of the terminology and components. These are further justifications for future research in this area to utilise qualitative inquiry.