American Psychiatric Association, Diagnostic and Statistical Manual of Mental Disorders, 4th-TR ed. (Washington, DC: Author, 2000).

James E. Barrett, et al. “The Prevalence of Psychiatric Disorders in a Primary Care Practice,” Archives of General Psychiatry 45, No. 12 (1988): 1100.

Robin M. Carter et al., “One-Year Prevalence of Subthreshold and Threshold DSM-IV Generalized Anxiety Disorder in a Nationally Representative Sample,” Depression and Anxiety 13, No. 2 (2001): 78.

John M. Hettema, Michael C. Neale, and Kenneth S. Kendler, “A Review and Meta-Analysis of the Genetic Epidemiology of Anxiety Disorders,” American Journal of Psychiatry 158 (2001): 1568.

Kenneth S. Kendler and Carol A. Prescott, Genes, Environment, and Psychopathology: Understanding the Causes of Psychiatric and Substance Use Disorders (New York: Guilford, 2006).

Barbara L. Kennedy and John J. Schwab, “Utilization of Medical Specialists by Anxiety Disorder Patients,” Psychosomatics 38, No. 2 (1997): 109.

Robert L. Leahy, “An Investment Model of Depressive Resistance,” Journal of Cognitive Psychotherapy: An International Quarterly 11 (1997): 3.

Robert L. Leahy and Stephen J. Holland, Treatment Plans and Interventions for Depression and Anxiety Disorders (New York: Guilford, 2000).

See Table 11-2 in S. Molina and T.D. Borkovec, “The Penn State Worry Questionnaire: Psychometric Properties and Associated Characteristics,” in Worrying: Perspectives on Theory Assessment and Treatment, eds. Graham C.L. Davey and Frank Tallis (Chichester, England: Wiley, 1994), 265–283.

Adrian Wells, “Meta-Cognition and Worry: A Cognitive Model of Generalized Anxiety Disorder,” Behavioural and Cognitive Psychotherapy 23 (1995) 301.

Adrian Wells and Gerald Matthews, “Modelling Cognition in Emotional Disorder: The S-REF model,” Behaviour Research and Therapy 34, No.11–12 (1996): 881.

Kimberly A. Yonkers et al., “Phenomenology and Course of Generalised Anxiety Disorder,” British Journal of Psychiatry 168 (1996): 308.