IMPORTANCE Self-guided internet-based cognitive behavioral therapy (iCBT) has the potential to increase access and availability of evidence-based therapy and reduce the cost of depression treatment.OBJECTIVES To estimate the effect of self-guided iCBT in treating adults with depressive symptoms compared with controls and evaluate the moderating effects of treatment outcome and response.DATA SOURCES A total of 13 384 abstracts were retrieved through a systematic literature search in PubMed, Embase, PsycINFO, and Cochrane Library from database inception to January 1, 2016.STUDY SELECTION Randomized clinical trials in which self-guided iCBT was compared with a control (usual care, waiting list, or attention control) in individuals with symptoms of depression. DATA EXTRACTION AND SYNTHESISPrimary authors provided individual participant data from 3876 participants from 13 of 16 eligible studies. Missing data were handled using multiple imputations. Mixed-effects models with participants nested within studies were used to examine treatment outcomes and moderators. MAIN OUTCOMES AND MEASURESOutcomes included the Beck Depression Inventory, Center for Epidemiological Studies-Depression Scale, and 9-item Patient Health Questionnaire scores. Scales were standardized across the pool of the included studies. RESULTSOf the 3876 study participants, the mean (SD) age was 42.0 (11.7) years, 2531 (66.0%) of 3832 were female, 1368 (53.1%) of 2574 completed secondary education, and 2262 (71.9%) of 3146 were employed. Self-guided iCBT was significantly more effective than controls on depressive symptoms severity (β = −0.21; Hedges g = 0.27) and treatment response (β = 0.53; odds ratio, 1.95; 95% CI, 1.52-2.50; number needed to treat, 8). Adherence to treatment was associated with lower depressive symptoms (β = −0.19; P = .001) and greater response to treatment (β = 0.90; P < .001). None of the examined participant and study-level variables moderated treatment outcomes.CONCLUSIONS AND RELEVANCE Self-guided iCBT is effective in treating depressive symptoms. The use of meta-analyses of individual participant data provides substantial evidence for clinical and policy decision making because self-guided iCBT can be considered as an evidence-based first-step approach in treating symptoms of depression. Several limitations of the iCBT should be addressed before it can be disseminated into routine care. M any studies [1][2][3][4] have found that depressive symptoms can be effectively treated with psychotherapy, pharmacotherapy, or both. Nevertheless, many people with depressive symptoms do not seek help, and even well-resourced health care systems find it difficult to marshal enough qualified therapists to offer psychological interventions. Access barriers to psychotherapy include limited availability of trained clinicians, high cost of treatment, and fear of stigmatization.5-8 As a consequence, a significant number of individuals with depressive symptoms remain untreated.9,10Self-guided internet-based cognitive behavioral therapy (iCBT) wi...

Psychotherapies may work through techniques that are specific to each therapy or through factors that all therapies have in common. Proponents of the common factors model often point to meta-analyses of comparative outcome studies that show all therapies have comparable effects. However, not all meta-analyses support the common factors model; the included studies often have several methodological problems; and there are alternative explanations for finding comparable outcomes. To date, research on the working mechanisms and mediators of therapies has always been correlational, and in order to establish that a mediator is indeed a causal factor in the recovery process of a patient, studies must show a temporal relationship between the mediator and an outcome, a dose–response association, evidence that no third variable causes changes in the mediator and the outcome, supportive experimental research, and have a strong theoretical framework. Currently, no common or specific factor meets these criteria and can be considered an empirically validated working mechanism. Therefore, it is still unknown whether therapies work through common or specific factors, or both.

We report the current best estimate of the effects of cognitive behavior therapy (CBT) in the treatment of major depression (MDD), generalized anxiety disorder (GAD), panic disorder (PAD) and social anxiety disorder (SAD), taking into account publication bias, the quality of trials, and the influence of waiting list control groups on the outcomes. In our meta-analyses, we included randomized trials comparing CBT with a control condition (waiting list, care-as-usual or pill placebo) in the acute treatment of MDD, GAD, PAD or SAD, diagnosed on the basis of a structured interview. We found that the overall effects in the 144 included trials (184 comparisons) for all four disorders were large, ranging from g50.75 for MDD to g50.80 for GAD, g50.81 for PAD, and g50.88 for SAD. Publication bias mostly affected the outcomes of CBT in GAD (adjusted g50.59) and MDD (adjusted g50.65), but not those in PAD and SAD. Only 17.4% of the included trials were considered to be high-quality, and this mostly affected the outcomes for PAD (g50.61) and SAD (g50.76). More than 80% of trials in anxiety disorders used waiting list control groups, and the few studies using other control groups pointed at much smaller effect sizes for CBT. We conclude that CBT is probably effective in the treatment of MDD, GAD, PAD and SAD; that the effects are large when the control condition is waiting list, but small to moderate when it is care-as-usual or pill placebo; and that, because of the small number of high-quality trials, these effects are still uncertain and should be considered with caution.Key words: Cognitive behavior therapy, major depression, generalized anxiety disorder, panic disorder, social anxiety disorder, meta-analysis, publication bias, quality of trials, waiting list control groups (World Psychiatry 2016;15:245-258) Every year almost 20% of the general population suffers from a common mental disorder, such as depression or an anxiety disorder 1 . These conditions not only result in personal suffering for patients and their families, but also in huge economic costs, in terms of both work productivity loss and health and social care expenditures 2-6 .Several evidence-based treatments are available for common mental disorders, including pharmacological and psychological interventions. Many patients receive pharmacological treatments, and these numbers are increasing in high-income countries 7 . Psychological treatments are equally effective in the treatment of depression 8 and anxiety disorders [9][10][11] . However, they are less available or accessible 12 , especially in low-and middle-income countries. At the same time, about 75% of patients prefer psychotherapy over the use of medication 13 . The most extensively tested form of psychotherapy is cognitive behavior therapy (CBT). Dozens of trials and several meta-analyses have shown that CBT is effective in treating depression 8,14 and anxiety disorders 9-11 . However, in recent years, it has become clear that the effects of CBT and other psychotherapies have been considerably ...