Ours was an uncontrolled (open) trial with outcome evaluation points post-treatment and 6 months post-treatment. The study protocol is supplied as an additional file.
Participants were required to be aged 18 or above and to have current bipolar mood instability, the definition of this being informed by DSM-V criteria for cyclothymic disorder (over the past 2 years numerous periods with hypomanic symptoms that do not meet criteria for a hypomanic episode and numerous periods with depressive symptoms that do not meet criteria for a depressive episode, continuing into the past month), and to be willing to engage in psychological therapy that focusses primarily on ongoing mood instability and its consequences. Because of the focus upon IMI as a trait that occurs across the bipolar spectrum, participants were required to meet DSM-IV  criteria for a bipolar spectrum condition (bipolar I disorder, bipolar II disorder, bipolar disorder not otherwise specified or cyclothymic disorder).
Patients were not able to participate in the study if they were currently experiencing mania or substance dependence disorder, were at high risk of attempting suicide (judged to be at immediate risk, according to the local research centre risk assessment tool), were currently receiving other psychological therapy, potentially placed other group members at significant risk (for example, through reported history of physical violence in similar settings) or lacked capacity to consent to research participation. Individuals presenting with another area of difficulty that the therapist and participant believed should be the primary focus of intervention (for example, prominent symptoms of post-traumatic stress disorder) were not included in the study, nor were individuals presenting with difficulties characteristic of borderline personality disorder rather than bipolar disorder (frequent and serious deliberate self-harm, marked disturbance in ability to form or maintain interpersonal relationships), as standard DBT is likely to be a more appropriate intervention for this group.
Potential participants were identified and approached by staff members in mental health assessment teams. Other than assessment, short-term support and medication advice, participants were not receiving ongoing secondary mental health care support.
As this was the first formal investigation of this subgroup, we did not pre-specify a target recruitment rate. Instead, we sought to use the findings to estimate recruitment rate for a subsequent controlled feasibility study. Informally, we considered that a recruitment rate of below two participants a month would be of concern for future studies because this would result in a long wait for participants to commence the group treatment.
We also surveyed clinicians from local mental health teams about their view of the therapy approach. A total of 10 clinicians participated in the survey, with four completing a brief semi-structured interview.
The intervention consisted of 16 sessions of group skills training, supported by individual meetings of up to 30 min that occurred approximately monthly for each person over the 4 months of group sessions. In addition, there were two “booster” group sessions at 3 and 6 months post-intervention.
Content of group sessions was informed by DBT and followed a modular format: mindfulness I (2 sessions), emotion regulation (5), mindfulness II (2), distress tolerance (2), interpersonal effectiveness (4) and consolidation (1). Content was developed in consultation with individuals with personal experience of bipolar disorder and followed five key principles of DBT: (i) clearly structured treatment; (ii) application of behavioural therapy; (iii) emphasis on validation of emotional response; (iv) dialectical stance, balancing acceptance and change; and (v) integration of mindfulness practice . Topics covered included skills for observing events, thoughts, emotions and bipolar symptoms without reacting impulsively, balancing lifestyle and activities to maximise mood stability and healthy rather than hypomanic positive mood, skills for downregulating emotion and negotiating interpersonal difficulties (which are often a consequence and a trigger of bipolar mood swings).
The group therapy sessions were delivered by two therapists. Individual sessions were with one of the two therapists, ensuring that all clients had the opportunity to meet separately with each therapist at least once during the programme. Therapy was delivered within a specialist psychological therapies service for adults with mood disorders.
In the current study, we ran the ThrIVe-B programme twice consecutively.
All participants were individuals diagnosed by their clinician as having (or probably having) bipolar or cyclothymic disorder. In addition, diagnosis was assessed by the research team using the structured clinical interview for DSM-IV , supervised by a clinical psychologist experienced in the use of the SCID.
Primary outcome measures: acceptability and feasibility
Acceptability of the therapy was measured in terms of (i) proportion of participants completing treatment (defined as attending at least 50% of the 16 group therapy sessions), (ii) participant ratings of treatment satisfaction, (iii) qualitative analysis of semi-structured interviews with participants at the end of therapy, (iv) clinician satisfaction ratings and (v) qualitative analysis of semi-structured interviews with clinicians. Overall participant satisfaction with the treatment was rated on a scale from 1 (very dissatisfied) to 4 (very satisfied); these data were collected as part of the standard service patient experience measure post-treatment. A more detailed measure of participant satisfaction was developed specifically for this study and asked participants, post-treatment and at follow-up, to rate their satisfaction on a scale from 1 (not at all) to 4 (very much so) with therapy content, group aspect, smartphone app, length of treatment, frequency of contact, fit with other commitments, discharge process and the ThrIVe-B programme. Neither measure has been externally validated.
Acceptability of the study procedures was addressed through qualitative analysis of the participant interviews and rates of completion of research measures. Feasibility was assessed via recruitment rate and qualitative analysis of interviews with clinicians.
Secondary outcome measures
Measures of symptoms
Manic symptoms were assessed using the 11-item, observer-rated Bech-Rafaelsen Mania Rating Scale (BMRS)  pre- and post-intervention. The BMRS has been shown to have adequate internal consistency and construct validity. The Altman Scale for Rating Mania (ASRM) , a five-item self-report measure of (hypo)manic symptom level, was completed on a session-by-session basis during the intervention: scores were used to inform and support therapy.
Depressive symptoms were measured using the nine-item Patient Health Questionnaire (PHQ9) , a widely used measure that can be used both to grade depressive symptom severity and establish probable presence of a major depressive episode pre- and post-intervention. The 21-item Beck Depression Inventory, second edition (BDI-II)  was also completed pre- and post-intervention, as well as on a session-by-session basis and at 6 months post-intervention.
Bipolar symptoms were also measured using the 16-item Internal State Scale (ISS) , which produces scores on four dimensions of depression, wellbeing, activation and perceived conflict.
Given high levels of anxiety amongst those with BD , the seven-item Generalised Anxiety Disorder Scale (GAD)  was used. As a general measure of psychiatric symptomatology, we included the 10-item Clinical Outcomes in Routine Evaluation Scale (CORE-10) .
Measures of sense of personal recovery and quality of life
The 36-item Bipolar Disorder Recovery Questionnaire (BDRQ)  was included as a measure of sense of personal recovery in people with bipolar disorder, as distinct from symptomatic or medical recovery. The BDRQ has been found to have adequate internal consistency and convergent validity. Finally, we included a measure of quality of life developed to be specific to individuals with bipolar disorder, the 12-item Brief Quality of Life in Bipolar Disorder scale (QoL.BD) .
Clinical process measures
Based upon the hypothesised core mechanisms of action of our intervention, we included measures of impulsive response to positive emotion (UPPS-P Impulsive Behaviour Scale ), avoidance behaviour (BADS: Behavioural Avoidance in Depression Scale ), mindfulness skills (KIMS: Kentucky Inventory of Mindfulness Skills ) and interpersonal functioning (IIP-32: Inventory of Interpersonal Problems—short version ). We also measured problematic beliefs about bipolar mood states (Brief-HAPPI: Brief Hypomanic Attitudes and Positive Predictions Inventory ) and a single-item asking about sense of fit with the group as social identification with treatment group may predict reduction of depression symptoms in individuals with unipolar depression . Participants used a purpose-built smartphone application during part of the therapy within which they rated their mood at least once daily and viewed coping suggestions they had pre-entered. Findings pertaining to the application are not reported here.
Intervention and trial safety
This was assessed through examination of (i) rate of symptom deterioration (overall and with respect to suicidality) and (ii) rate of serious adverse events judged to be a consequence of the therapy or trial.
After giving written, informed consent to a member of the study team, participants completed a research interview including relevant sections of the SCID to determine study eligibility. Eligible participants wishing to continue then completed the acceptability, outcome and process measures. All participants used the monitoring app for 1 week prior to the first group therapy session. Participants returned completed BDI-II and ASRM measures to each group therapy session. Mid-way through the programme, participants completed the process measures.
Following the final group therapy session, participants completed a post-treatment interview including the SCID mood disorders section for the period since initial assessment, and the acceptability, outcome and process measures.
Six months after the end of the intervention phase, participants completed the SCID mood disorders section for the period since the previous assessment, the BDI-II and ASRM and measures of quality of life (QoL.BD), recovery (BDRQ) and acceptability of the intervention.
We aimed to recruit sufficient numbers for two iterations of the therapy programme, with each therapy group containing between 4 and 8 participants.
Because of the absence of a comparator arm, neither participants nor assessors were blind to participant allocation.
Descriptive statistics were used to summarise participant flow through the study and responses on quantitative measures of acceptability. To examine changes on clinical and process measures, means and standard deviations were calculated, as were effect sizes of change in scores from pre- to post-treatment [(μ2 − μ1)/pre-treatment SD]. For each participant, reliable change in their scores from pre- to post-treatment was calculated using the reliable change index (RCI: SEdiff = SD1√2 √1 − r) . Analyses were per protocol (PP: including only those attending at least 50% of sessions) and intention to treat (ITT), using all data available, regardless of treatment received. Bivariate correlations were conducted to examine pre-post correlations within measures.
Qualitative data were subjected to thematic analysis. Transcripts from interviews with participants were coded by one rater, and a preliminary thematic framework developed. The transcripts were then coded by a second rater using the framework. Discrepancies in coding, and modifications to the framework, were discussed and a joint framework agreed. The transcripts were then recoded by rater 2 following the agreed framework.
Transcripts from interviews with staff were subjected to thematic analysis by a single rater and common themes identified.