The National Comorbidity Survey in the US, based on DSM-III-R, reported 12-month prevalence estimates of 3.1 %, and lifetime prevalence estimates of 5.1 % with women being twice as likely to suffer from GAD as men (Wittchen et al, 1994). The recent Australian National Survey of Mental Health and Well Being used DSM-IV criteria and obtained a 12-month prevalence estimate of 3.6 % (Hunt, 2002). A survey using the broader criteria of ICD-10 reported lifetime prevalence rates of 8.9 % (World Health Organization, 1993). Looking at the evidence as a whole Tyrer (1999) concluded that around 10 % of the population have an anxiety disorder of some sort at any one time with GAD being the most common presentation. Subthreshold presentations of generalised anxiety are clearly much more common than episodes of disorder. It is also important to remember that anxiety disorders are amongst the most prevalent psychiatric disorders of childhood (Bernstein et al, 1996) and there is evidence that GAD is the most prevalent of the anxiety disorders diagnosed later in life (Stanley & Novy, 2000).
Age of onset may be as early as 13 years when presenting as a primary disorder and as late as 30 years when presentation is secondary to other disorders (Rogers et al., 1999). The mean age of onset has been estimated at 21 years (Yonkers et al., 1996) although the average age of referral to specialist services is in middle age (Ballenger etal., 2001). Most cases are managed in primary care in which setting it is a common and often chronic disorder (Goldberg & Lecrubier, 1995; Noyes et al., 1992). In a substantial proportion of those with GAD, chronic worry and tension are clearly lifelong problems with symptom severity waxing and waning in response to social and environmental stressors (Blazer et al., 1987; Noyes et al., 1992). The average length of particular episodes has been estimated to be 20 years (Yonkers et al., 1996) which greatly exceeds the six-month duration required for DSM-IV.
There is growing evidence that chronic anxiety is associated with increased risk for medical illness (Greenberg et al., 1999). Indeed, it may be a fundamental vulnerability factor in the aetiology of a range of psychiatric disorders but particularly depression and alcohol abuse (Fava et al., 2000; Judd et al., 1998). It is estimated to cause psychosocial disability of a similar magnitude to that of chronic somatic disease (Ormel et al., 1994) and depression (Wittchen et al., 2000). There is also evidence that comorbidity between GAD and other conditions increases the rate of attempted suicide (Lecrubier, 1998). In short, the overall evidence supports the view that GAD is a significant public health problem.
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