Effective elements of cognitive behaviour therapy for psychosis: results of a novel type of subgroup analysis based on principal stratification

Abstract

BackgroundMeta-analyses show that cognitive behaviour therapy for psychosis (CBT-P) improves distressing positive symptoms. However, it is a complex intervention involving a range of techniques. No previous study has assessed the delivery of the different elements of treatment and their effect on outcome. Our aim was to assess the differential effect of type of treatment delivered on the effectiveness of CBT-P, using novel statistical methodology.MethodThe Psychological Prevention of Relapse in Psychosis (PRP) trial was a multi-centre randomized controlled trial (RCT) that compared CBT-P with treatment as usual (TAU). Therapy was manualized, and detailed evaluations of therapy delivery and client engagement were made. Follow-up assessments were made at 12 and 24 months. In a planned analysis, we applied principal stratification (involving structural equation modelling with finite mixtures) to estimate intention-to-treat (ITT) effects for subgroups of participants, defined by qualitative and quantitative differences in receipt of therapy, while maintaining the constraints of randomization.ResultsConsistent delivery of full therapy, including specific cognitive and behavioural techniques, was associated with clinically and statistically significant increases in months in remission, and decreases in psychotic and affective symptoms. Delivery of partial therapy involving engagement and assessment was not effective.ConclusionsOur analyses suggest that CBT-P is of significant benefit on multiple outcomes to patients able to engage in the full range of therapy procedures. The novel statistical methods illustrated in this report have general application to the evaluation of heterogeneity in the effects of treatment.

Evaluation and validation of social and psychological markers in randomised trials of complex interventions in mental health: a methodological research programme

“…This answers the question 'What factors make the treatment work better?'. For example, how might the treatment effect be influenced by characteristics of the therapeutic process such as the amount of therapy received (sessions attended), adherence to treatment protocols (the fidelity/validity of the treatment received 13 ) or the strength of the therapeutic alliance between therapist and patient? 14 Although they are modifiers of the effects of treatment, such process measures are integral to the therapy (they do not precede the therapy) and cannot be regarded as predictive markers or treatment moderators.…”

“…70,71 In principle, principal stratification can easily be extended to cope with categorical process measures with three or more unordered categories. Dunn et al, 13 for example, considered non-compliers (those who never turned up for CBT), participants who attended (or would have attended) their CBT sessions but did not receive the CBT as intended (being more akin to supportive listening) and participants who received (or would have received) CBT as intended. Here it was thought to be legitimate to introduce the exclusion restriction for the non-compliers but the model was still underidentified.…”

“…high or low alliance) but latent in the control group. Following Dunn et al, 13 we include those from the treated group with missing alliance data but acknowledge that their stratum status is hidden, just as for the control group (assuming that conditional on the baseline covariates, the distribution of alliance status is not dependent on whether or not it is observed). We illustrate the details in the following section.…”

Opening the Black Box of Cognitive-Behavioural Case Management in Clients with Ultra-High Risk for Psychosis

“…CBT-informed therapy is an umbrella term for a plethora of different strategies that has primarily been evaluated as an overall “treatment package” [10] which, in clinical implementation, is carried out in a variety of forms [11,12]. CBT comprises various components such as psychoeducation, case formulation, cognitive challenging, or behavioural strategies.…”

“…CBT comprises various components such as psychoeducation, case formulation, cognitive challenging, or behavioural strategies. Little is known, especially in the field of at-risk mental states, about which components of CBT are in fact delivered and if there are specific CBT “ingredients” which may be more beneficial than others [10,13]. Furthermore, the effects of frequency or intensity of CBT (i.e., number of sessions delivered) on treatment outcome has only been partially investigated [4].…”