Objectives. We investigated the treatment effects reported from a high-quality randomized controlled trial of cognitive behavioural therapy (CBT) for 106 people with borderline personality disorder attending community-based clinics in the UK National Health Service - the BOSCOT trial. Specifically, we examined whether the amount of therapy and therapist competence had an impact on our primary outcome, the number of suicidal acts(dagger), using instrumental variables regression modelling.
Design. Randomized controlled trial. Participants from across three sites (London, Glasgow, and Ayrshire/ Arran) were randomized equally to CBT for personality disorders (CBTpd) plus Treatment as Usual or to Treatment as Usual. Treatment as Usual varied between sites and individuals, but was consistent with routine treatment in the UK National Health Service at the time. CBTpd comprised an average 16 sessions (range 0-35) over 12 months.
Method. Weused instrumental variable regression modelling to estimate the impact of quantity and quality of therapy received (recording activities and behaviours that took place after randomization) on number of suicidal acts and inpatient psychiatric hospitalization. Results. A total of 101 participants provided full outcome data at 2 years post randomization. The previously reported intention-to-treat (ITT) results showed on average a reduction of 0.91 (95% confidence interval 0.15-1.67) suicidal acts over 2 years for those randomized to CBT. By incorporating the influence of quantity of therapy and therapist competence, we show that this estimate of the effect of CBTpd could be approximately two to three times greater for those receiving the right amount of therapy from a competent therapist.
Conclusions. Trials should routinely control for and collect data on both quantity of therapy and therapist competence, which can be used, via instrumental variable regression modelling, to estimate treatment effects for optimal delivery of therapy. Such estimates complement rather than replace the ITT results, which are properly the principal analysis results from such trials.
|Number of pages||14|
|Journal||Psychology and Psychotherapy: Theory Research and Practice|
|Early online date||19 Feb 2013|
|Publication status||Published - Sept 2013|
The authors thank the 106 participants who made the study possible, and the other members of the BOSCOT research team (see Davidson, Tyrer et al., 2006b for a complete roll call). The authors declare they have no conflict of interests of any description in publishing these results. BOSCOT was funded by the Wellcome Trust (064027/Z/01/Z). The funder played no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; or the preparation, review, or approval of the manuscript. Kate Davidson (Chief Investigator) and John Norrie (Study Statistician) take responsibility for the integrity of the data and accuracy of the data analysis, and we confirm that all authors had full access to all the data in the study.