• Recognize the public relevance of mental disorders worldwide
  
• Understand indicators of the frequency, the impact and the use of services in relation to mental disorders
  
• Stimulate the search for additional information and knowledge about solutions needed to diminish the global burden of mental disorders

As health care spending continues to rise, treatment resource allocation decisions will need to be based increasingly on information about the prevalence and societal burden of illness. Interest in societal burden has increased dramatically over the past decade based on this recognition and as part of a larger movement to rationalize the allocation of treatment resources and maximize benefit in relation to cost. Much of the current interest in mental disorders among health policy makers is based on the fact that these disorders have consistently been found in studies of disease burden to be both among the most burdensome health problems in the world1 and also to be among the disorders with the lowest ratio of investments in treatment to disease burdens.2

A number of factors account for the high burden of mental disorders. They are commonly occurring, often begin at an early age, often are quite persistent throughout the life course, and often have substantial adverse effects on functioning. The low investments in treatment are more difficult to explain but presumably are due at least partly to failure of health policymakers to recognize the high prevalence and burden of mental disorders.

Data are here presented from the World Health Organization (WHO) World Mental Health (WMH) surveys initiative.3 This initiative was launched to diminish the information gap regarding the high prevalence and burden of mental disorders, with the specific objectives of assessing the prevalence, severity, and comparative societal burden of mental disorders throughout the world. Although the WMH is still a work in progress, enough useful information has been produced to warrant a review of data produced by WMH up to now on the global epidemiology of common mental disorders.

WMH includes a series of geographically representative mental health surveys carried out in all major regions of the world. A key aim of the surveys is to help countries that would not otherwise have the expertise or infrastructure to implement high-quality community epidemiologic surveys that can be used for health policy planning purposes by providing centralized instrument development, training, and data analysis (www.hcp.med.harvard.edu/wmh). Twenty-eight countries have so far completed WMH surveys. The vast majority of these surveys are nationally representative, although a few are representative of only a single region (e.g., the São Paolo metropolitan area in Brazil) or regions (e.g., six metropolitan areas in Japan). The details about sampling in the countries that have been analyzed for the present analyses are shown in Table 17-1.

All WMH surveys use the same diagnostic interview, the WHO Composite International Diagnostic Interview (CIDI).4 The CIDI is a state-of-the-art fully structured research diagnostic interview designed to be used by trained lay interviewers who do not have any clinical experience to diagnose mood disorders, anxiety disorders, behavior disorders, and substance use disorders. Consistent interviewer training materials, training programs, and quality control monitoring procedures are used to guarantee comparability across all WMH surveys. Consistent WHO translation, back translation, and harmonization procedures for the interview text and training materials are also used across countries. Methodological studies have documented good concordance between diagnoses based on the CIDI and blinded clinical diagnoses.5

The CIDI was designed to go well beyond the mere assessment of mental disorders to include a wide range of measures about important correlates of these disorders. For purposes of this report, two of these extensions are of special importance. One is that the CIDI includes disorder-specific measures of role impairment that are administered in exactly the same fashion for each mental disorder in the surveys as well as for each of a wide variety of chronic physical disorders assessed for comparison purposes in the surveys. These measures, a modified version of the Sheehan Disability Scales (SDS), assess condition-specific role impairments in four role domains: home management, work, social life, and personal relationships. Previous methodological studies have documented good internal consistency reliability across the SDS domains,6,7 a result that was replicated in the WMH data both in developed and developing countries.1

Second, the CIDI assesses not only disorder prevalence but also disorder severity. This is important in light of the finding in previous epidemiologic surveys that quite a high proportion of the general population in many countries meets criteria for a Diagnostic and Statistical Manual of Mental Disorders (DSM) or International Classification of Diseases mental disorder.8–10 Faced with this high prevalence, mental health policy planning efforts need to consider disorder severity for treatment planning purposes because the simple presence of a diagnosis may not indicate need for services. All WMH respondents who were classified as meeting criteria for one or more mental disorders at some time in the 12 months before the interview were consequently classified either as serious, moderate, or mild cases. Serious cases were defined as those with nonaffective psychosis, bipolar I disorder, or substance dependence with a physiologic dependence syndrome; those who made a serious suicide attempt (i.e., not merely a suicide gesture); those that reported severe role impairment due to their mental illness in at least two areas of functioning measured by the SDS; and those having overall functional impairment due to their mental illness consistent with a Global Assessment of Functioning (GAF)11 score of 50 or less. Disorders not classified serious were classified as moderate if they included substance dependence without a physiologic dependence syndrome; or at least moderate interference on the SDS in at least one disorder-specific scale of role impairment. All other disorders were classified as mild.

A comment is required about diagnostic coverage before turning to results. Almost all previous community epidemiologic surveys of common mental disorders focused on mood disorders (major depression, dysthymia, bipolar disorder), anxiety disorders (generalized anxiety disorder [GAD], panic disorder, phobia, obsessive-compulsive disorder, posttraumatic stress disorder [PTSD]), and substance use disorders (alcohol and drug abuse and dependence). The WMH surveys expanded this list to include disruptive behavior disorders (attention-deficit/hyperactivity disorder, conduct disorder, oppositional-defiant disorder, and intermittent explosive disorder). Nonaffective psychoses (NAP) including, for example, schizophrenia, schizophreniform disorder, schizoaffective disorder, delusional disorder and brief psychotic reaction have also been included in a number of community epidemiologic surveys (e.g., Kessler et al, 2005; Ochoa et al, 2008; Gureje et al, 2010),12–14 but the sensitivity of survey measures of NAP is so low that great caution is needed in interpreting results. Data on NAP are consequently not reviewed here, although a screen for NAP was included in many of the WMH surveys. Excellent reviews of the literature on the epidemiology of NAP are available elsewhere.15,16 In addition, Axis II personality disorders have generally not been included in community epidemiologic surveys of mental disorders. Although some preliminary data exist on the epidemiology of these disorders17 and a number of WMH surveys included screens for personality disorders,18 these data are not reviewed here because they are so sparse.

Prevalence of Common Mental Disorders in the WMH Surveys

The WMH surveys that have been completed so far (which are only a subset of the 28 in the initiative) show clearly that the mental disorders assessed in the CIDI are quite common in all the countries studied. 12-month prevalence estimates, that is estimates of the proportion of respondents who met criteria for one or more of the mental disorders assessed in the surveys at some time in the year prior to the interview, are presented here. The 12-month prevalence estimates average 9.7% for any anxiety disorder with an interquartile range (IQR) (25th to 75th percentiles) across countries of 6.6 to 13.7 (Table 17-2). Mood disorders are generally found to be the next most prevalent class of disorders, with 12-month prevalence estimates for any mood disorder in the WMH surveys averaging 5.5%, with an IQR of 3.4 to 7.0. Prevalence estimates of anxiety and mood disorders are generally higher in Western developed countries than in developing countries.

The 12-month prevalence estimates for substance disorders (0.2% to 6.4%; IQR: 1.2% to 3.5%) and disruptive behavior disorders (0.1% to 10.5%; IQR: 1.1% to 3.5%) are consistently lower than for anxiety or mood disorders. It is noteworthy, though, that some WMH surveys did not assess illicit drug abuse or dependence, possibly leading to artificially low prevalence estimates compared with other countries. Substance dependence was also assessed only in the presence of abuse, possibly further reducing estimated prevalence.19

Noticeable international variation exists in the 12-month prevalence of the mental disorders assessed in the WMH surveys. The lowest prevalence estimates are in Nigeria (6%), Beijing/Shanghai metropolitan area (7.1%), and Japan (7.4%); the highest are in São Paulo (29.6%), the United States (27%), and Northern Ireland (23.1%). In general, countries/regions with low prevalences show lower frequencies of all types of disorders. Explanations of international variations in the prevalence of mental disorders have long been discussed.20 Among several issues, cultural relevance of mental diagnoses and severity of cases have been raised as possible explanations for cross-national variation in prevalence estimates. These issues are addressed in the next section.

Severity of Mental Disorders

Many previous epidemiologic surveys estimated disorder prevalence, but the WMH surveys are the first ones to generate systematic estimates of disorder severity. As mentioned earlier, in the WMH analyses the severity of mental disorders is categorized as serious, moderate, and mild, taking into account information on the type of disorder, the degree of impairment, and the presence of suicide ideation. The proportions of respondents with a constellation of 12-month DSM-IV/CIDI disorders classified as either serious (7.2% to 36.8%; IQR: 18.5% to 25.7%) or moderate (12.5% to 50.6%; IQR: 33.0% to 42.3%) in the first set of completed WMH surveys, using the definitions of those terms described earlier, are generally smaller than the proportions with mild disorders (Table 17-3). The severity distribution among cases varies significantly across countries (p < 0.001), with severity not strongly related either to region or to development status. The unconditional 12-month prevalence estimate of serious mental illness in the WMH surveys is in the range of 4.0% to 6.8% for half the surveys, 2.3% to 3.6% for another quarter, and 0.8% to 1.9% for the final quarter.

There are substantial positive associations across surveys between overall prevalence of any disorder and both the proportion of cases classified as serious (Pearson r = 0.40, p < 0.005) and the proportion of cases classified as either serious or moderate (Pearson r = 0.50, p < 0.001). These positive associations are important because they address an issue that has been raised in the methodological literature regarding the possibility of biased prevalence estimates. Two separate research groups found a pattern opposite the one found in the WMH surveys, leading them to argue that prevalence estimates are biased in some epidemiologic surveys. One of these groups, based in Korea, compared results from their Korean Epidemiologic Catchment Area (KECA) Study21

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