Epidemiology of Anxiety Disorders - Conclusion
The authors would like to end by the beginning, referring to the caveats in the introduction of the present chapter. There are still other matters of concern: the frequent use of lay interviewers in major surveys, recall bias in interviews over lifetime span, the key issue of defining a threshold for clinical significancy, just to name a few.
It follows that in spite of the apparent evidence, extreme caution should be exercised when interpreting the epidemiology of anxiety.
Post-Traumatic Stress Disorder (PTSD)
The DSM-IV definition for PTSD contains criteria for (a) the traumatic experience; (b) re-experiencing; (c) avoidance of associated stimuli and numbing; and (d) increased arousal. Duration of symptoms should be at least one month (e); and (f ) distress or impairment in functioning is required (APA, 1994). When PTSD was first defined in DSM-III (APA, 1980), the original stressor criterion characterised traumatic experiences as being outside the range of human experience. However, when the prevalence of such events was systematically examined, it became apparent that trauma is surprisingly commonplace. Several studies have investigated the overall prevalence of traumatic events in the general population, looking both at communitybased populations and populations of individuals at high risk of trauma or exposed to events such as natural disasters (Acierno et al., 1999). The nature of the trauma can be very diverse, such as childhood abuse, traffic accidents, fires, violent assault, robberies and floods or earthquakes.
Prevalence
Prevalence rates have increased from DSM-III to DSM-III-R and DSM-IV. Also, in some telephone interview surveys prevalence is much higher, and in studies among young persons where recall bias may be minimal. Kessler et al. (1995) reported on the National Comorbidity Survey of 5877 persons, aged 15 to 54 years. The estimated lifetime prevalence of PTSD was found to be 7.8%.
Generalised Anxiety Disorder (GAD)
The concept of generalised anxiety disorder is subject to discussion. Although the disorder is regarded as prevalent in primary care as well as in specialised settings, because of the high comorbidity rates associated with GAD the controversy is about whether to consider GAD an independent disorder or as a residual or prodrome of other disorders (Wittchen et al., 1994). The diagnostic category of GAD has changed a lot in the past two decades (Brawman-Mintzer and Lydiard, 1996). The shifting diagnostic criteria, the relative low diagnostic reliability, and questions regarding the diagnostic validity probably contributed to the relative little attention that has been paid to the investigation of GAD compared with most other anxiety disorders.
Prevalence
The most recent epidemiological study using DSM-III-R criteria is the NCS in the United States. The prevalence rate for current GAD was 1.6%, 12-month prevalence was 3.1% and lifetime prevalence was 5.1% (Wittchen et al., 1994). These figures make GAD more common than panic disorder in the NCS. It is shown that GAD is more common in primary care, and one of the least common anxiety disorders in mental health centres (Brawman-Mintzer and Lydiard, 1996).
Obsessive-Compulsive Disorder (OCD)
Obsessive-compulsive disorder is defined as the presence of recurrent obsessions (persistent thoughts, impulses, or images) or compulsions (repetitive behaviour or thought patterns induced in an attempt to prevent anxiety) that are excessively time-consuming (taking more than an hour a day) or cause marked distress or significant impairment. The subject recognises that these patterns are excessive.
Differential diagnosis of obsessive-compulsive disorder includes generalised anxiety disorder, panic disorder, phobias, compulsive personality disorder, and hypochondriasis. While many of these syndromes are characterised by intrusive thoughts, few have associated rituals. The complex tics seen in some patients with Tourette’s syndrome may be difficult to distinguish from the compulsions seen in obsessive-compulsive disorder, and, in fact, there is significant overlap in symptoms between the two disorders (Rasmussen and Eisen, 1992).