Epidemiology and Comorbidity
Current data indicate that GAD is probably one of the more com-mon psychiatric disorders. The National Comorbidity Survey (NCS) of psychiatric disorders (Kessler et al., 1994) found preva-lence rates of 1.6% for current GAD (defined as the most recent 6-month period of anxiety), 3.1% for 12-month GAD, and 5.1% for lifetime GAD, with lifetime prevalence higher in females (6.6%) than males (3.6%). The more recent National Comorbidity Survey replication (NCS-R) found a lifetime prevalence of 5.7% (Kessler et al., 2005 GAD appears at even higher rates in clinical settings, par-ticularly in primary care settings. For example, Shear and col-leagues (1994) found prevalence rates of GAD, using DSM-III-R criteria, reported by patients at four primary care centers, to be twice as high as those reported in community samples (i.e., 10 versus 5.1%). Similarly, a collaborative study by the World Health Organization (WHO) across 15 international sites reported prev-alence rates of GAD at approximately 8% in primary care set-tings (Maier et al., 2000).
Those with anxiety symptoms meeting criteria for GAD in the Epideiological Catchment Area (ECA) study reported re-ceiving more outpatient mental services during the previous year than those diagnosed with other psychiatric disorders (Blazer et al., 1991). Many of those with GAD in the National Comorbidity Survey sought professional help for GAD (66% of participants) and used medications to reduce their symptoms of GAD (44% of participants). Over 80% of the GAD group in the Harvard/ Brown Anxiety Disorders Research Program (HARP) data indi-cated that they received psychotherapy and/or pharmacotherapy (Yonkers et al., 1996).
Rates of GAD appear similar in special populations such as children and the elderly. GAD appears to be less prevalent in children than in adults. Data from the NCS indicate that for both lifetime and 12-month prevalence rates, GAD occurs at the low-est rate in younger ages and at the highest rate in older adults Epidemiological data on prevalence of GAD in childhood using DSM-IV criteria are currently lacking. In the elderly, GAD ap-pears to account for the majority of anxiety disorders, with prev-alence rates ranging from 0.7 to 7.3%.
Although it is unclear whether childhood GAD predis-poses to the development of adult GAD or represents an early manifestation of adult GAD, these studies further suggest that generalized anxiety is highly prevalent both in the community and in the clinical population.