Large-scale epidemiological studies

Large-scale epidemiological studies have given us, for the first time, a detailed view about the current and lifetime prevalence of MDD. In what is probably the best of these studies in the United States (called the National Comorbidity Survey), the lifetime prevalence of MDD, as defined by the American Psychiatric Association's DSM-III-R criteria, was estimated at 17%. This same survey found that nearly 5% of the population reported meeting criteria for MDD in the last 30 days (Blazer et al. 1994). As has long been suspected, MDD is probably the most common of psychiatric disorders and, indeed, among the most common of major biomedical conditions in “first-world” countries such as the United States. Consensus, however, has not been reached about the single best estimate of population risk, as other studies have reported rates both substantially lower and somewhat higher than those reported in the National Comorbidity Survey. As is true in other areas of epidemiologic research, response patterns to interviews are sensitive to the specific wording of items, techniques used to motivate “effortful responding” and the organization of the assessment instrument.

The field of psychiatric epidemiology has identified a substantial list of putative risk factors for MDD. As in any nonexperimental subject, one difficulty has been to discriminate association from causation. Four risk factors stand out in the consistency of their association with MDD and the level of evidence suggesting that at least some of the association is indeed causal: gender, stressful life events, adverse childhood experiences, and certain personality traits. Across many studies, varying widely in time and place, women have been shown to be at consistently greater risk for MDD than men. In most studies, the ratio of prevalence rates in women to men has been in the range of 1.5 to 2.5. In the National Comorbidity Study, the lifetime prevalence of MDD in the US population was estimated to be 21.3% in women and 12.7% in men (Blazer et al. 1994). A wide range of environmental adversities such as job loss, marital difficulties, major health problems, and loss of close personal relationships are associated with a substantial increase in risk for the onset of MDD (Kessler 1997). A range of difficulties in childhood including physical and sexual abuse, poor parent-child relationships, and parental discord and divorce almost certainly increase the risk for MDD later in life. Certain kinds of personality traits appear to predispose to MDD, with the best evidence available for the trait termed “Neuroticism.” Neuroticism, first proposed by the British psychologist Eysenck, is a stable personality trait that reflects the predisposition to develop emotional upset under stress. A range of other risk factors has been proposed for MDD, although in general the evidence for the existence of a causal association is weaker. These would include low social class, urban residence, separated or divorced marital status, low levels of social support, and being in a more recently born age group. A recent WHO report (Murray and Lopez 1996) ranked depression as the fourth medical condition with the greatest disease burden worldwide, measured in Disability-Adjusted Life Years, which express years of life lost to premature death and years lived with a disability of specified severity and duration. The same report predicted that depression would be the second condition with the greatest disease burden worldwide by 2020 (Murray and Lopez 1996).

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Large-scale epidemiological studies have, given us for the first time a detailed, view about the current and lifetime prevalence. Of MDD. In what is probably the best of these studies in the United States (called the National Comorbidity Survey), the. Lifetime prevalence of MDD as defined, by the American Psychiatric Association 's, DSM-III-R criteria was estimated at 17%.This same survey found that nearly 5% of the population reported meeting criteria for MDD in the last 30 days (Blazer et. Al. 1994). As has long, been suspected MDD is probably the most common of psychiatric disorders and indeed among the most,,, Common of major biomedical conditions in "first-world." countries such as the United States. Consensus however,,Has not been reached about the single best estimate of population risk as other, studies have reported rates both substantially. Lower and somewhat higher than those reported in the National Comorbidity Survey. As is true in other areas of epidemiologic. Research response patterns, to interviews are sensitive to the specific wording, of itemsTechniques used to motivate "effortful responding." and the organization of the assessment instrument.

The field of psychiatric. Epidemiology has identified a substantial list of putative risk factors for MDD. As in any, nonexperimental subject one. Difficulty has been to discriminate association from causation.Four risk factors stand out in the consistency of their association with MDD and the level of evidence suggesting that. At least some of the association is indeed causal: gender stressful events, life, childhood, adverse experiences and certain. Personality traits. Across many studies varying widely, in time, and place women have been shown to be at consistently greater. Risk for MDD than men.In most studies the ratio, of prevalence rates in women to men has been in the range of 1.5 to 2.5. In the National Comorbidity. Study the lifetime, prevalence of MDD in the US population was estimated to be 21.3% in women and 12.7% in men (Blazer et. Al. 1994). A wide range of environmental adversities such as job loss marital difficulties major health problems,,,And loss of close personal relationships are associated with a substantial increase in risk for the onset of MDD (Kessler. 1997). A range of difficulties in childhood including physical and sexual abuse poor parent-child relationships and parental,,, Discord and divorce almost certainly increase the risk for MDD later in life. Certain kinds of personality traits appear. To predispose, to MDD