title: Heterogeneity in patient-reported outcomes following low-intensity mental health interventions: a multilevel analysis.
abstract: BACKGROUND
  Variability in patient-reported outcomes of psychological treatments has been partly attributed to therapists--a phenomenon commonly known as therapist effects. Meta-analytic reviews reveal wide variation in therapist-attributable variability in psychotherapy outcomes, with most studies reporting therapist effects in the region of 5% to 10% and some finding minimal to no therapist effects. However, all except one study to date have been conducted in high-intensity or mixed intervention groups; therefore, there is scarcity of evidence on therapist effects in brief low-intensity psychological interventions.
  
  
  OBJECTIVE
  To examine therapist effects in low-intensity interventions for depression and anxiety in a naturalistic setting.
  
  
  METHODS
  Session-by-session data on patient-reported outcome measures were available for a cohort of 1,376 primary care psychotherapy patients treated by 38 therapists. Outcome measures included PHQ-9 (sensitive to depression) and GAD-7 (sensitive to general anxiety disorder) measures. Three-level hierarchical linear modelling was employed to estimate therapist-attributable proportion of variance in clinical outcomes. Therapist effects were evaluated using the intra-cluster correlation coefficient (ICC) and Bayesian empirical predictions of therapist random effects. Three sensitivity analyses were conducted: 1) using both treatment completers and non-completers; 2) a sub-sample of cases with baseline scores above the conventional clinical thresholds for PHQ-9 and GAD-7; and 3) a two-level model (using patient-level pre- and post-treatment scores nested within therapists).
  
  
  RESULTS
  The ICC estimates for all outcome measures were very small, ranging between 0% and 1.3%, although most were statistically significant. The Bayesian empirical predictions showed that therapist random effects were not statistically significantly different from each other. Between patient variability explained most of the variance in outcomes.
  
  
  CONCLUSIONS
  Consistent with the only other study to date in low intensity interventions, evidence was found to suggest minimal to no therapist effects in patient-reported outcomes. This draws attention to the more prominent source of variability which is found at the between-patient level.
authors.affiliation: Department of Health Sciences, University of York, York, United Kingdom; Centre for Health Economics, University of York, York, United Kingdom.
authors.forename: Shehzad
authors.initials: S
authors.lastname: Ali
authors.affiliation: Department of Health Sciences, University of York, York, United Kingdom.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Littlewood
authors.affiliation: Department of Health Sciences, University of York, York, United Kingdom.
authors.forename: Dean
authors.initials: D
authors.lastname: McMillan
authors.affiliation: Primary Care Mental Health Service, Leeds Community Healthcare NHS Trust, Leeds, United Kingdom.
authors.forename: Jaime
authors.initials: J
authors.lastname: Delgadillo
authors.affiliation: Centro de Investigación y Docencia Económicas, Mexico City, Mexico.
authors.forename: Alfonso
authors.initials: A
authors.lastname: Miranda
authors.affiliation: Department of Health Sciences, University of York, York, United Kingdom.
authors.forename: Tim
authors.initials: T
authors.lastname: Croudace
authors.affiliation: Department of Health Sciences, University of York, York, United Kingdom.
authors.forename: Simon
authors.initials: S
authors.lastname: Gilbody
mesh_terms: D000328:Adult; D001008:Anxiety Disorders / Q000503:physiopathology / Q000523:psychology / Q000628:therapy*; D001499:Bayes Theorem; D003863:Depression / Q000503:physiopathology / Q000523:psychology / Q000628:therapy*; D003866:Depressive Disorder / Q000503:physiopathology / Q000523:psychology / Q000628:therapy*; D005260:Female; D006801:Humans; D008297:Male; D008603:Mental Health; D008875:Middle Aged; D055361:Multilevel Analysis; D063868:Patient Outcome Assessment; D011613:Psychotherapy / Q000706:statistics & numerical data*; D006113:United Kingdom