Christensen et al JOURNAL OF MEDICAL INTERNET RESEARCH Review Adherence in Internet Interventions for Anxiety and Depression: Systematic Review Helen Christensen, PhD, MPsych, BA; Kathleen M Griffiths, PhD, BSci; Louise Farrer, BPsych Centre for Mental Health Research, The Australian National University, Canberra, Australia Corresponding Author: Helen Christensen, PhD, MPsych, BA Centre for Mental Health Research Australian National University Canberra ACT 0200 Australia Phone: +61 2 6125 8409 Fax: +61 2 6125 0733 Email: Helen.Christensen@anu.edu.au Abstract Background: Open access websites which deliver cognitive and behavioral interventions for anxiety and depression are characterised by poor adherence. We need to understand more about adherence in order to maximize the impact of Internet-based interventions on the disease burden associated with common mental disorders. Objective: The aims of this paper are to review briefly the adherence literature with respect to Internet interventions and to investigate the rates of dropout and compliance in randomized controlled trials of anxiety and depression Web studies. Methods: A systematic review of randomized controlled trials using Internet interventions for anxiety and depression was conducted, and data was collected on dropout and adherence, predictors of adherence, and reasons for dropout. Results: Relative to reported rates of dropout from open access sites, the present study found that the rates of attrition in randomized controlled trials were lower, ranging from approximately 1 - 50%. Predictors of adherence included disease severity, treatment length, and chronicity. Very few studies formally examined reasons for dropout, and most studies failed to use appropriate statistical techniques to analyze missing data. Conclusions: Dropout rates from randomized controlled trials of Web interventions are low relative to dropout from open access websites. The development of theoretical models of adherence is as important in the area of Internet intervention research as it is in the behavioral health literature. Disease-based factors in anxiety and depression need further investigation. (J Med Internet Res 2009;11(2):e13) doi: 10.2196/jmir.1194 KEYWORDS Patient dropouts; depression; depressive disorder, major; anxiety disorders; Internet; mental health services; treatment outcome Introduction less than 1% of users completed all modules in an open access website for depression. Web-based interventions are effective for a range of mental health disorders including depression, panic, post-traumatic stress disorder (PTSD), perceived stress in schizophrenia, stress, insomnia, and eating disorders [1]. While efficacy trials of Web interventions show good-to-excellent levels of adherence, open access websites have been associated with poor adherence and dropout, with substantial numbers of users not completing all Web pages and exiting websites before the full completion of an offered program [2,3]. For example, Farvolden [4] found that only 1% of participants completed a 12-week open access panic program, and Christensen and colleagues [5] reported that There is little reason to expect that the rates of adherence to websites offered as open access on the Web would be as strong as those reported for websites which are examined in the context of an efficacy trial. Open access websites provide information and Web content directly to community users at no, or minimal, cost. Data on adherence from these sites