Acceptance and commitment therapy (ACT) is a 'third wave' behaviour therapy that has been building an evidence base to suggest that it is a promising and useful psychotherapy across a wide range of diagnoses (for reviews see Hayes, Luoma, Bond, Masuda, \& Lillis, 2006; Powers, Zum, \& Emmelkamp, 2009; Ruiz, 2010; Öst. 2014). ACT is grounded in relational frame theory (RFT; Hayes, 2004) and seeks to define how patients become overly emotionally influenced by internal dialogues, to the point of being immune to positive environmental contingencies (Ciarrochi, Bilich, \& Godsel, 2010). The main aim of ACT is to enable psychological flexibility, so that a patient is able to fully connect to the present moment and to also alter (or continue with) behaviours closely aligned to personal values (Hayes et al., 1999). The goal of ACT is to teach skills of handling unwanted/avoided thoughts/feelings to reduce their impact/influence and clarifying what is truly important and meaningful, then using that knowledge to guide, inspire, and motivate continued valued actions in the effort to enrich personal lives (Hayes, 2004).

Psychological flexibility is achieved through six core processes during ACT; defusion; acceptance; contact with the present moment; values; committed action and self-as-context (Hayes, Strosahl, \& Wilson, 2012). These components are combined in the 'hexaflex' model (Rolffs, Rogge \& Wilson, 2018). Strosahl, Hayes,Wilson, and Gifford (2004) however stated that there was clinically no predefined order for focusing on the processes and not all individuals needed to concentrate on each of the processes to achieve flexibility. There are a variety of in-session and between-session exercises for each aspect of the hexaflex that support patients in understanding, practicing and using the relevant psychological skills (e.g. Hayes et al., 1999).

The ACT model discriminates between three aspects or levels of self; self-as-content, self-as-process, and self-as-context (Hayes et al., 2012). Self-as-content refers to the contents of psychological experience, self-as-process refers to awareness of the on-going changing nature of experiences and self-as-context refers to experiential contact with a persistent and unchanging perspective from which all experiences are observed (De Houwer, Roche, \& Dymond, 2013). During ACT, patients learn to build awareness of self-as-context, whilst simultaneously letting go of any over-attachment to a conceptualised self. Self-as-context is independent of content and is the place from which content is observed (Ciarrochi, et al., 2010). The 'I' of self-as-context statements is learnt to be appreciated as stable/constant, in order to retain a sense of self in the face of stress (Pierson et al., 2004) and to appreciate that self-evaluations are transient and temporary (Hayes et al., 1999). Hayes et al (2012) postulated that the ability to occupy a self-as-context position requires self-as-process to be learnt first

The last several decades of psychotherapy outcome research have mainly focussed on gauging the efficacy of 'complete' psychotherapies (i.e. the 'package' of treatment). Whilst this approach has proved useful in some psychotherapies being then recognized as empirically validated, it has simultaneously failed to identify which aspects of the package that are essential, redundant or possibly harmful (Rosen \& Davison, 2003). This 'package approach' has also been criticised for promoting the proliferation of apparently 'new' psychotherapies that are essentially re-packages of extant psychotherapies (Ciarrochi et al., 2010). Therefore, despite extensive outcome research validating psychotherapy as an effective treatment (e.g. Roth \& Fonagy, 2006), research has been slower to identify the necessary, effective and active ingredients of each individual psychotherapy. Therefore, proving the utility of these different active ingredients (and associated definitive technical features) is a key challenge to the psychotherapy outcome literature (Crits-Christoph, 1997; Stevens, Hynan, \& Allen, 2000). Research is therefore necessary that unpacks and compares the components of any psychotherapy 'package' to then assess their relative and specific contribution to outcomes (Stevens et al., 2000).

Two methodological approaches have been previously used to dismantle, isolate and define the importance of specific components within ACT's hexaflex; mediation studies and lab-based component analyses. Mediation analyses index changes in putative processes between treatments, and so identifies the clinical utility of theoretically distinct components (Kraemer, Wilson, Fairburn, \& Agras, 2002). However, only a small number of core ACT processes have been examined in mediation studies (namely acceptance and cognitive defusion; see Stockton et al., 2019 for a recent review). Lab-based studies have compared performance on tasks when participants are provided with instructions grounded in a component of the hexaflex (or 'control' instructions) and a meta-analysis has shown small-to-medium effect sizes for 4/6 hexaflex components (Levin, Hildebrandt, Lillis, \& Hayes, 2012). No lab-based studies have been conducted on the committed action or self-as-context components (Levin, Hildebrandt, Lillis, \& Hayes, 2012). The clinical trial design used to test the efficacy of components of psychotherapies are labelled as either a deconstruction or an additive study (Ahn \& Wampold. 2001). Dismantling designs compare a whole treatment, with treatment minus a specific theoretically important component (e.g. Jacobson et al., 1996). Additive designs test the impact of providing a specific and supplementary component hypothesised to enhance outcomes (e.g. Propst, Ostrom, Watkins, Dean, \& Mashburn, 1992). No clinical dismantling trials of ACT's hexaflex have been attempted.

RFT provides the theoretical basis for the importance of self-as-context as a component of the hexaflex, as this component is believed to enable and facilitate engagement with the other core processes of the hexaflex (Hayes, 2004). There is however an on-going debate as to whether development of self-as-context is necessary during ACT to enable flexibility, or whether it is sufficient to only develop self-as-process (De Houwer et al., 2013; McHugh \& Stewart, 2012). This is the first study to use a deconstruction method to examine the efficacy of the self-as-context component of the psychological flexibility model. Given that the ethical and therapeutic impact of extracting a potentially clinically important hexaflex component has been previously untested, the current study adopted a pilot trial approach. The scientific value of pilot studies that examine the feasibility, safety and effectiveness of new treatments (or in the current context, a deconstructed partial treatment) is widely recognised (Arain, Campbell, Cooper \& Lancaster, 2010). The study used participants with a long-term health condition (LTC) and concurrent mental health problems, in terms of their ability to engage in psychological flexibility, decentering and also clinical outcome. Patients with LTCs were seen as an appropriate patient group for the present study, as previous evidence has attested to the effectiveness of ACT with this patient group (Levin et al., 2012). The hypotheses for the study were that participants receiving full ACT would (a) display enhanced ability to engage in psychological flexibility and decentering and (b) achieve better clinical outcomes.