For the clinical psychiatrist, the most disabling and important conditions are schizophrenia, other functional psychoses and dementia. However, from the perspective of public health, depression and anxiety are very common and, though less disabling for the patients, lead in aggregate to more disability in the population as a whole. Of course, there is much evidence for a strong association between depression and disability in both developed and less developed countries [3-5]. Common mental disorders have also been linked to diminished productivity and sickness absence. These statistics reflect observations all too familiar to practising clinicians in primary care and psychiatry.
Despite the empirical and clinical evidence for a substantial population disability associated with depression, it has proved difficult to establish depression as a public health priority. Public health priorities have relied mainly upon comparisons of mortality statistics and have neglected conditions that lead to morbidity. The World Bank attempted to address this deficit by adopting a methodology that calculated the Disability Adjusted
Life Years (DALYs) lost to various diseases. This approach was designed to enable morbidity and mortality to be compared and therefore allow a rational setting of public health priorities.
The idea behind the DALY is to estimate the proportion of a year that should be attributable to a variety of conditions causing morbidity. If someone dies prematurely, then each year lost counts as one whole DALY. If someone has an illness, such as depression, then each year affected by illness will count as a proportion of a DALY. The controversial and difficult aspect of this method is in estimating the proportion that should be used when calculating DALYs for non-fatal conditions. The first estimates were very subjective, but more recent attempts have been made to base these estimates on a firmer empirical footing . A further limitation concerns the quality of the data on prevalence. Much of the epidemiological information that has been used to estimate the burden of diseases around the world is of questionable reliability, particularly in relation to developing countries, where few large-scale surveys on representative samples have been carried out.
The World Development Report and associated publications [7-9] have provided the first estimates that have allowed comparison between depression, other mental disorders and physical illness leading to death. The report estimated that neuropsychiatric disorders led to 8% of the Global Burden of Disease (GBD). For adults aged 15 to 44, mental disorders are estimated to account for 12% of the GBD. Mental disorders are projected to increase to 15% of the GBD and major depression is expected to become second only to ischaemic heart disease in terms of disease burden by the year 2020 .
Mental disorders have received little priority in the developing world. Demographic transition and improved measures to combat infectious diseases are leading to a change in the pattern of disease in many poor countries . In Chile, for example, life expectancy is now over 70 years and, along with many other areas of the world, the burden of disease is largely produced by non-communicable diseases familiar to those in the West. These changes will contribute to the growing importance of depression and other mental disorders in world health.
The Global Burden of Disease Study  has succeeded in putting depression on the public health map. What has proved more difficult is to persuade policy makers to attend to depression or to encourage research that will lead to a better understanding of the aetiology of depression. Depression is as big a potential public health issue as ischaemic heart disease. For the latter, some major risk factors are well known and preventive strategies can be proposed and are often implemented. In contrast, little is known about the aetiology of depression and in particular there is little evidence for strategies that would lead to primary prevention of depression.
In the following sections of the chapter we shall discuss the influence of globalization on socio-economic status and then gender, and its implications for mental health. In particular, we shall discuss some of the empirical findings in relation to depression and anxiety, as these are the most important psychiatric conditions from the perspective of public health.
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