title: Effective elements of cognitive behaviour therapy for psychosis: results of a novel type of subgroup analysis based on principal stratification.
abstract: BACKGROUND
  Meta-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.
  
  
  METHODS
  The 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.
  
  
  RESULTS
  Consistent 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.
  
  
  CONCLUSIONS
  Our 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.
authors.affiliation: Health Sciences Research Group, School of Community-Based Medicine, University of Manchester, UK. graham.dunn@manchester.ac.uk
authors.forename: G
authors.initials: G
authors.lastname: Dunn
authors.forename: D
authors.initials: D
authors.lastname: Fowler
authors.forename: R
authors.initials: R
authors.lastname: Rollinson
authors.forename: D
authors.initials: D
authors.lastname: Freeman
authors.forename: E
authors.initials: E
authors.lastname: Kuipers
authors.forename: B
authors.initials: B
authors.lastname: Smith
authors.forename: C
authors.initials: C
authors.lastname: Steel
authors.forename: J
authors.initials: J
authors.lastname: Onwumere
authors.forename: S
authors.initials: S
authors.lastname: Jolley
authors.forename: P
authors.initials: P
authors.lastname: Garety
authors.forename: P
authors.initials: P
authors.lastname: Bebbington
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015928:Cognitive Behavioral Therapy / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008131:London; D008297:Male; D008875:Middle Aged; D011569:Psychiatric Status Rating Scales; D011618:Psychotic Disorders / Q000523:psychology / Q000628:therapy*; D055502:Secondary Prevention; D016896:Treatment Outcome; D055815:Young Adult