title: Frequency and change mechanisms of psychotherapy among depressed patients: study protocol for a multicenter randomized trial comparing twice-weekly versus once-weekly sessions of CBT and IPT.
abstract: BACKGROUND
  Cognitive behavioral therapy (CBT) and interpersonal therapy (IPT) are among the most well established therapies for the treatment of depression. However, some major questions remain unanswered. First, it is unknown what session frequency results in the most optimal (cost) effectiveness in psychotherapy. Second, the debate as to what mechanisms underlie the effect of psychotherapy has not yet been resolved. Enhancing knowledge about the optimal session frequency and mechanisms of change seems crucial in order to optimize the (cost) effectiveness of psychotherapy for depression. This study aims to compare treatment outcome of twice-weekly versus once-weekly sessions of CBT and IPT. We expect twice-weekly sessions to be more effective and lead to more rapid recovery of depressive symptoms in comparison to once-weekly sessions. Both therapy-specific and non-specific process measures will be included to unravel the mechanisms of change in psychotherapy for depression. Besides the use of self-reports and behavioral observations, this study will also examine underlying biological processes by collecting blood samples.
  
  
  METHODS
  In a multicenter randomized trial, two hundred depressed patients will be recruited from Dutch specialized mental healthcare centers and randomized into one of the following groups, all receiving a maximum of 20 sessions in different frequencies: a) twice-weekly sessions at the start of CBT, b) twice-weekly sessions at the start of IPT, c) once-weekly sessions at the start of CBT, d) once-weekly sessions at the start of IPT. Primary outcome measures are depression severity, cost-effectiveness and quality of life. Process measures include therapeutic alliance, recall, therapy-specific skills, motivation and compliance. Assessments will take place during baseline, monthly during treatment and follow-up at month 9, 12 and 24. In addition, at 12 and 24 months, the frequency of depressive episodes in the previous year will be assessed. Blood samples will be taken pre- and post-treatment. The study has been ethically approved and registered.
  
  
  CONCLUSIONS
  Finding that twice-weekly sessions are more effective or lead to more rapid recovery of depressive symptoms could lead to treatment adaptations that have the potential to reduce the personal and societal burden of depression. In addition, insight into the mechanisms of change and physiological processes in psychotherapy will enable us to optimize treatments and may help to understand human functioning beyond the context of treatment.
  
  
  BACKGROUND
  The study has been registered on October 21th, 2014 at the Netherlands Trial Register, part of the Dutch Cochrane Centre ( NTR4856 ).
authors.affiliation: Department of Clinical Psychology, VU University Amsterdam, and EMGO Institute, Amsterdam, The Netherlands. s.j.e.bruijniks@vu.nl.
authors.forename: Sanne J E
authors.initials: SJ
authors.lastname: Bruijniks
authors.affiliation: Department of Health Sciences, EMGO Institute for Health and Care Research, Faculty of Earth and Life Sciences, Section of Health Economics and Health Technology Assessment, VU University Amsterdam, Amsterdam, The Netherlands. j.e.bosmans@vu.nl.
authors.forename: Judith
authors.initials: J
authors.lastname: Bosmans
authors.affiliation: Department of Psychiatry and Psychology, University Hospital Maastricht; School for Mental Health and Neuroscience, Faculty of Health, Medicine and Life Sciences, Maastricht University, Maastricht, Netherlands. f.peeters@maastrichtuniversity.nl.
authors.forename: Frenk P M L
authors.initials: FP
authors.lastname: Peeters
authors.affiliation: Department of Psychology, Vanderbilt University, Nashville, Tennessee, USA. steven.d.hollon@vanderbilt.edu.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Hollon
authors.affiliation: Department of Psychiatry, VU Medical Centre/GGZ ingeest, and the EMGO Institute, Amsterdam, The Netherlands. p.vanoppen@ggzingeest.nl.
authors.forename: Patricia
authors.initials: P
authors.lastname: van Oppen
authors.affiliation: PsyQ, Parnassia Groep, Hague, Netherlands. M.vandenBoogaard@psyq.nl.
authors.forename: Michael
authors.initials: M
authors.lastname: van den Boogaard
authors.affiliation: Altrecht Institute for Mental Health Care, Utrecht, Netherlands. p.dingemanse@altrecht.nl.
authors.forename: Pieter
authors.initials: P
authors.lastname: Dingemanse
authors.affiliation: Department of Clinical Psychology, VU University Amsterdam, and EMGO Institute, Amsterdam, The Netherlands. p.cuijpers@vu.nl.
authors.forename: Pim
authors.initials: P
authors.lastname: Cuijpers
authors.affiliation: Department of Clinical Psychology, University of Amsterdam, Amsterdam, The Netherlands. A.R.Arntz@uva.nl.
authors.forename: Arnoud
authors.initials: A
authors.lastname: Arntz
authors.affiliation: Trimbos-institute, Netherlands Institute of Mental Health and Addiction, Utrecht, The Netherlands. gfranx@trimbos.nl.
authors.forename: Gerdien
authors.initials: G
authors.lastname: Franx
authors.affiliation: Department of Clinical Psychology, VU University Amsterdam, and EMGO Institute, Amsterdam, The Netherlands. m.j.h.huibers@vu.nl.
authors.forename: Marcus J H
authors.initials: MJ
authors.lastname: Huibers
mesh_terms: D000328:Adult; D000368:Aged; D002985:Clinical Protocols; D015928:Cognitive Behavioral Therapy / Q000379:methods*; D003362:Cost-Benefit Analysis; D003863:Depression / Q000097:blood / Q000628:therapy*; D005260:Female; D006801:Humans; D008297:Male; D009426:Netherlands; D010349:Patient Compliance; D011614:Psychotherapy, Brief / Q000379:methods*; D016896:Treatment Outcome; D055815:Young Adult