title: Effectiveness of Internet-Based Interventions for the Prevention of Mental Disorders: A Systematic Review and Meta-Analysis.
abstract: Mental disorders are highly prevalent and associated with considerable disease burden and personal and societal costs. However, they can be effectively reduced through prevention measures. The Internet as a medium appears to be an opportunity for scaling up preventive interventions to a population level.
  
  
  
  The aim of this study was to systematically summarize the current state of research on Internet-based interventions for the prevention of mental disorders to give a comprehensive overview of this fast-growing field.
  
  
  
  A systematic database search was conducted (CENTRAL, Medline, PsycINFO). Studies were selected according to defined eligibility criteria (adult population, Internet-based mental health intervention, including a control group, reporting onset or severity data, randomized controlled trial). Primary outcome was onset of mental disorder. Secondary outcome was symptom severity. Study quality was assessed using the Cochrane Risk of Bias Tool. Meta-analytical pooling of results took place if feasible.
  
  
  
  After removing duplicates, 1169 studies were screened of which 17 were eligible for inclusion. Most studies examined prevention of eating disorders or depression or anxiety. Two studies on posttraumatic stress disorder and 1 on panic disorder were also included. Overall study quality was moderate. Only 5 studies reported incidence data assessed by means of standardized clinical interviews (eg, SCID). Three of them found significant differences in onset with a number needed to treat of 9.3-41.3. Eleven studies found significant improvements in symptom severity with small-to-medium effect sizes (d=0.11- d=0.76) in favor of the intervention groups. The meta-analysis conducted for depression severity revealed a posttreatment pooled effect size of standardized mean difference (SMD) =-0.35 (95% CI, -0.57 to -0.12) for short-term follow-up, SMD = -0.22 (95% CI, -0.37 to -0.07) for medium-term follow-up, and SMD = -0.14 (95% CI, -0.36 to 0.07) for long-term follow-up in favor of the Internet-based psychological interventions when compared with waitlist or care as usual.
  
  
  
  Internet-based interventions are a promising approach to prevention of mental disorders, enhancing existing methods. Study results are still limited due to inadequate diagnostic procedures. To be able to appropriately comment on effectiveness, future studies need to report incidence data assessed by means of standardized interviews. Public health policy should promote research to reduce health care costs over the long term, and health care providers should implement existing, demonstrably effective interventions into routine care.
authors.affiliation: Institute of Psychology, Depatment of Rehabilitationpsychology and Psychotherapy, University of Freiburg, Freiburg, Germany. lasse.sander@psychologie.uni-freiburg.de.
authors.forename: Lasse
authors.identifier: 0000-0002-4222-9837
authors.initials: L
authors.lastname: Sander
authors.forename: Leonie
authors.identifier: 0000-0002-8113-5438
authors.initials: L
authors.lastname: Rausch
authors.forename: Harald
authors.identifier: 0000-0002-2040-661X
authors.initials: H
authors.lastname: Baumeister
keywords: Internet and mobile-based; mental disorders; meta-analysis; prevention; systematic review