ساختار پنهان اختلال اضطراب فراگیر در افراد میانسال

Generalized anxiety disorder (GAD) is identified as a discrete disorder in the DSM-5, but evidence suggests that GAD and the related construct of pathological worry possesses a dimensional latent structure. The objective of this study was to ascertain the latent structure of GAD using taxometric methods. A subsample of adults (N=2061) from the Midlife in the United States Study, a national sample of Americans, provided the data. Additional data from individuals who were re-interviewed 10 year later (n=1228) were also analyzed. Items corresponding to the DSM-IV-TR diagnostic criteria for GAD were used to generate indicators for the taxometric analyses. Multiple taxometric procedures provided no evidence that GAD has a categorical or taxonic latent structure. Instead, the results were more consistent with the proposition that GAD exists on a continuum. Evidence that GAD is dimensional suggests that dichotomizing individuals into GAD versus non-GAD groups will typically result in decreased statistical power. They also suggest that any diagnostic thresholds for identifying GAD are likely to be arbitrary. The findings are consistent with models that locate GAD within the framework of extant dimensional models of personality and with research that emphasizes a multifactorial etiology for GAD.

The question of whether psychiatric disorders represent qualitatively distinct conditions (analogous to strep throat) or whether they identify the extreme ends of dimensional continua (analogous to most forms of Type II diabetes) is fundamental to psychiatric taxonomy. This question is especially pertinent to the diagnosis of generalized anxiety disorder (GAD) because it is defined by an excess of symptoms that are common in everyday life, such as anxiety, worry, and tension. Do individuals with GAD represent a unique taxon who suffer from a qualitatively distinct/pathological form of anxiety and worry, or are they at the far end of a continuum of anxiety and worry? In the latter instance, GAD may be the manifestation of high trait anxiety (Rapee, 1991) or neuroticism (Hettema et al., 2004). This question of latent structure can be addressed directly using a set of taxometric procedures developed by Meehl and colleagues (Meehl and Yonce, 1994 and Waller and Meehl, 1998). Although two published studies have used taxometric methods to examine the latent structure of worry, a review commissioned by the DSM-5 Anxiety, Obsessive–compulsive Spectrum, Posttraumatic, and Dissociative Disorders Work Group found that “there have been no published studies of the latent structure of GAD” and recommended that “the structure of the full syndrome will need to be evaluated directly” (Andrews et al., 2010, p. 143). Similarly, in his review of taxometric studies of psychiatric disorders, Haslam (2007) concluded that it was uncertain whether generalized anxiety was dimensional or taxonic. Most recently, a comprehensive review of 177 taxometric studies of psychopathology and personality found 60 taxometric findings regarding anxiety disorders, including studies that examined the latent structure of worry, but none specifically examined GAD (Haslam et al., 2012). Most taxometric studies that have examined the latent structure of anxiety-related constructs have yielded dimensional findings (Haslam et al., 2012). Three papers examined constructs more closely related to GAD. Ruscio et al. (2001) examined the latent structure of worry in a large sample of college students. Items from the Penn State Worry Questionnaire (PSWQ; Meyer et al., 1990) and the worry-related items from another measure of GAD served as the indicators of worry. Their analyses yielded consistent evidence that worry has a dimensional latent structure. Olatunji et al. (2010) examined the latent structure of worry in both a large community sample and a large undergraduate sample, using indicators drawn from the PSWQ and other measures of worry and anxiety. Consistent with the findings from Ruscio et al. (2001), Olatunji et al. (2010)found that worry had a dimensional latent structure in both samples. Somewhat complicating these findings, a taxometric study of a large sample of military recruits reported finding evidence of an anxiety taxon (Kotov et al., 2005). However, the indicators used for these analyses were drawn from the Beck Anxiety Inventory (BAI; Steer et al., 1993), the Vulnerability Scale (Schmidt et al., 1995), and an Anxiety Impairment Scale that the authors designed for their study. The BAI, which provided two of the four indicators for the taxometric analyses, primarily assesses autonomic arousal symptoms and panic (Cox et al., 1996), which are not central features of GAD (Brown et al., 1998). Furthermore, none of these measures focused on the primary symptoms of GAD, such as worry, tension, and fatigue. Therefore, even if an anxiety taxon exists, it is unlikely that this taxon is isomorphic with GAD. Although excessive worry is the cardinal symptom of anxiety, most individuals who report high levels of worry do not meet the diagnostic criteria for GAD (Ruscio, 2002). Therefore, it is possible that whereas worry may have a dimensional structure, GAD may be categorical (i.e., in the same way that influenza is a taxonic condition even though one of its hallmark symptoms, elevated body temperature, is dimensional). Additionally, with the exception of one community sample with a mean age of 33.5 (Olatunji et al., 2010, Study 1), all of these other taxometric studies have assessed samples of college students and other young adults. However, GAD prevalence rates appear to peak between the ages of 35 and 54 (Hunt et al., 2002). Therefore, a taxometric study using a mid-life sample may be most appropriate for determining the latent structure of GAD. If GAD is taxonic, a study of middle-aged individuals would be most likely to identify this putative taxon and dimensional results from such a study would carry greater probative weight than studies with young adult samples. A related issue is that because GAD has a relatively low prevalence rate, taxometric studies with non-clinical samples run the risk of missing a low base rate taxon. Previous studies have somewhat mitigated this risk by using large samples (N>1000). In the current study, we not only used a very large sample (N>2000), but also limited the sample to individuals who reported excessive worry. These sampling procedures increased the base rate of GAD in the sample and reduced the likelihood of failing to identify a GAD taxon if one was present. Finally, if GAD is taxonic, it is reasonable to expect taxon membership to remain relatively stable over time (cf. Watson, 2003). Using a longitudinal data set, in which respondents were re-assessed 10 years after their initial interviews, allowed us to examine whether the latent structure of GAD was consistent at both time points. Furthermore, if GAD was taxonic, we would be able to examine whether taxon membership remained consistent over 10 years. Thus, as the first study to examine the latent structure of GAD in a longitudinal sample of middle-age adults who reported excessive worry, the current study may provide more definitive conclusions about the latent structure of GAD.