The aim of this study is to estimate the lifetime and 12-month prevalence, severity and treatment of Diagnostic and Statistical Manual of Mental Disorders fourth edition (DSM-IV) mental disorders in Japan based on the final data set of the World Mental Health Japan Survey conducted in 2002–2006.

Face-to-face household interviews of 4130 respondents who were randomly selected from Japanese-speaking residents aged 20 years or older were conducted from 2002 to 2006 in 11 community populations in Japan (overall response rate, 56%). The World Mental Health version of the World Health Organization Composite International Diagnostic Interview (WMH-CIDI), a fully structured, lay administered psychiatric diagnostic interview, was used for diagnostic assessment.

Lifetime/12-month prevalence of any DSM-IV common mental disorders in Japan was estimated to be 20.3/7.6%. Rank-order of four classes of mental disorders was anxiety disorders (8.1/4.9%), substance disorders (7.4/1.0%), mood disorders (6.5/2.3%) and impulse control disorders (2.0/0.7%). The most common individual disorders were alcohol abuse/dependence (7.3/0.9%), major depressive disorder (6.1/2.2%), specific phobia (3.4/2.3%) and generalized anxiety disorder (2.6/1.3%). While the lifetime prevalence of any mental disorder was greater for males and the middle-aged, the persistence (proportion of 12-month cases among lifetime cases) of any mental disorder was greater for females and younger respondents. Among those with any 12-month disorder, 15.3% were classified as severe, 44.1% moderate and 40.6% mild. Although a strong association between severity and service use was found, only 21.9% of respondents with any 12-month disorder sought treatment within the last 12 months; only 37.0% of severe cases received medical care. The mental health specialty sector was the most common resource used in Japan. Although the prevalence of mental disorders were quite low, mental disorders were the second most prevalent cause of severe role impairment among chronic physical and mental disorders.

These results suggest lower prevalence of mental disorders in Japan than that in Western countries, although the general pattern of disorders, risk factors and unmet need for treatment were similar to those in other countries. Greater lifetime prevalence for males and greater persistence for females seems a unique feature of Japan, suggesting a cultural difference in gender-related etiology and course of disorders. The treatment rate in Japan was lower than that in most other high-income countries in WMH surveys.

Suppose you are the developer of a new therapy for a mental health problem or you have several years of experience working with such a therapy, and you would like to prove that it is effective. Randomised trials have become the gold standard to prove that interventions are effective, and they are used by treatment guidelines and policy makers to decide whether or not to adopt, implement or fund a therapy.

You would want to do such a randomised trial to get your therapy disseminated, but in reality your clinical experience already showed you that the therapy works. How could you do a trial in order to optimise the chance of finding a positive effect?

Methods that can help include a strong allegiance towards the therapy, anything that increases expectations and hope in participants, making use of the weak spots of randomised trials (risk of bias), small sample sizes and waiting list control groups (but not comparisons with existing interventions). And if all that fails one can always not publish the outcomes and wait for positive trials.

Several methods are available to help you show that your therapy is effective, even when it is not.

People with serious mental illness are increasingly turning to popular social media, including Facebook, Twitter or YouTube, to share their illness experiences or seek advice from others with similar health conditions. This emerging form of unsolicited communication among self-forming online communities of patients and individuals with diverse health concerns is referred to as peer-to-peer support. We offer a perspective on how online peer-to-peer connections among people with serious mental illness could advance efforts to promote mental and physical wellbeing in this group.

In this commentary, we take the perspective that when an individual with serious mental illness decides to connect with similar others online it represents a critical point in their illness experience. We propose a conceptual model to illustrate how online peer-to-peer connections may afford opportunities for individuals with serious mental illness to challenge stigma, increase consumer activation and access online interventions for mental and physical wellbeing.

People with serious mental illness report benefits from interacting with peers online from greater social connectedness, feelings of group belonging and by sharing personal stories and strategies for coping with day-to-day challenges of living with a mental illness. Within online communities, individuals with serious mental illness could challenge stigma through personal empowerment and providing hope. By learning from peers online, these individuals may gain insight about important health care decisions, which could promote mental health care seeking behaviours. These individuals could also access interventions for mental and physical wellbeing delivered through social media that could incorporate mutual support between peers, help promote treatment engagement and reach a wider demographic. Unforeseen risks may include exposure to misleading information, facing hostile or derogatory comments from others, or feeling more uncertain about one's health condition. However, given the evidence to date, the benefits of online peer-to-peer support appear to outweigh the potential risks.

Future research must explore these opportunities to support and empower people with serious mental illness through online peer networks while carefully considering potential risks that may arise from online peer-to-peer interactions. Efforts will also need to address methodological challenges in the form of evaluating interventions delivered through social media and collecting objective mental and physical health outcome measures online. A key challenge will be to determine whether skills learned from peers in online networks translate into tangible and meaningful improvements in recovery, employment, or mental and physical wellbeing in the offline world.

There are only a small number of prospective studies that have systematically evaluated standardised diagnostic criteria for mental disorder for more than a decade. The aim of this study is to present the approximated overall and sex-specific cumulative incidence of mental disorder in the Zurich cohort study, a prospective cohort study of 18–19 years olds from the canton of Zurich, Switzerland, who were followed through age 50.

A stratified sample of 591 participants were interviewed with the Structured Psychopathological Interview and Rating of the Social Consequences of Psychological Disturbances for Epidemiology, a semi-structured interview that uses a bottom-up approach to assess the past-year presence of 15 psychiatric syndromes. Seven interview waves took place between 1979 and 2008. Approximated cumulative incidence was estimated using Kaplan–Meier methods.

Rates of mental disorder were considerably higher than those generally reported in cross-sectional surveys. We found rates ranging from 32.5% for major depressive disorder to 1.2% for Bipolar I disorder. The cumulative probability of experiencing any of the mental disorders assessed by age 50 was 73.9%, the highest reported to date. We also found that rates differed by sex for most disorders, with females generally reporting higher rates of mood, anxiety and phobic disorder, and males reporting higher rates of substance- and alcohol-related disorders.

These findings confirm those of other long-term prospective studies that indicate the nearly universal nature of disturbances of emotion and behaviour across the life span. Greater community awareness of the normative nature of these experiences is warranted. An important area of future research is study long-term course and stability to determine who among those with such disturbances suffer from chronic disabling mental disorders. Such longitudinal studies may aid in directing services and intervention efforts where they are most needed.