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 ...

These results suggest that the effects of psychotherapy for depression are small, above the threshold that has been suggested as the minimal important difference in the treatment of depression, and Eysenck was probably wrong. However, this is still not certain because we could not adjust for all types of bias. Unadjusted meta-analyses of psychotherapies overestimate the effects considerably, and for several types of psychotherapy for adult depression, insufficient evidence is available that they are effective because too few low-risk studies were available, including problem-solving therapy, interpersonal psychotherapy and behavioural activation.

BackgroundDepression during adolescence is a serious mental health problem. Difficulties in regulating evoked emotions after stressful life events are considered to lead to depression. This study examined if depressive symptoms were mediated by various cognitive emotion regulation strategies after stressful life events, more specifically, the loss of a loved one, health threats or relational challenges.MethodsWe used a sample of 398 adolescents (Mage = 16.94, SD = 2.90), including 52 depressed outpatients, who all reported stressful life event(s). Path analyses in Mplus were used to test mediation, for the whole sample as well as separately for participants scoring high versus low on depression, using multigroup analyses.ResultsHealth threats and relational challenging stressful life events were associated with depressive symptoms, while loss was not. More frequent use of maladaptive strategies was related to more depressive symptoms. More frequent use of adaptive strategies was related to less depressive symptoms. Specific life events were associated with specific emotion regulation strategies. The relationship between challenging, stressful life events and depressive symptoms in the whole group was mediated by maladaptive strategies (self-blame, catastrophizing and rumination). No mediation effect was found for adaptive strategies.ConclusionThe association between relational challenging, stressful life events and depressive symptoms was mediated by maladaptive, cognitive emotion regulation strategies.