Interest in the study of anxiety disorders has increased dramatically since the publication of the third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III; American Psychological Association (APA), 1980). In fact, the 1980s witnessed a 10-fold increase in the number of published articles devoted to the study of anxiety disorders (Norton et al., 1995), and anxiety disorders were the topic of 14% of the articles published in clinical psychology and psychiatry journals between 1990 and 1992 (Cox et al., 1995). The large majority of these studies focused on panic disorder (McNally, 1994) and social phobia (Heimberg et al., 1995). However, investigations of generalized anxiety disorder (GAD) have recently begun to appear with increasing frequency (Borkovec et al., 1991; Brownand Barlow, 1992; Wittchen et al., 1994).
Compared to other anxiety disorders, GAD remains poorly understood. Advances in understanding have been slowed by the evolving definition of the disorder. In DSM-III, GAD was a residual category that could not be diagnosed in the presence of any other anxiety or affective disorder (APA, 1980). Attempts to diagnose GAD according to DSM-III criteria were also characterized by low inter-rater reliability (Barlow, 1987). However, the diagnostic criteria for GAD changed substantially from DSM-III to DSM-IV (APA, 1994). GAD is no longer considered to be a residual category, but a disorder specifically characterized by excessive and uncontrollable worry and somatic symptoms suggestive of central nervous system hyperarousal (e.g., muscle tension).