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Abstract
The anxiety disorders are common, costly, chronic and frequently co-occur. Despite the existence of effective treatments many people have difficulty accessing evidence-based treatment. Two innovative strategies that may reduce barriers to treatment include internet-delivered cognitive-behavioural therapy (iCBT) and transdiagnostic treatments. iCBT treatments are highly structured interventions, comprising systematically presented online lessons, homework, and supplementary resources. Transdiagnostic treatments target core symptoms underlying conditions such as depression and anxiety disorders, and aim to treat comorbid symptoms. An aim of this thesis was to develop and evaluate a transdiagnostic iCBT intervention, the Anxiety Program, for three anxiety disorders. Using a randomised controlled trial (RCT) design, Study 1 found that treatment using the Anxiety Program was associated with improvement across a range of generic and disorder-specific measures, relative to a waitlist control group. Using an enhanced version of the Anxiety Program, a second RCT (Study 2) demonstrated that the intervention was efficacious for all three disorders and also demonstrated that support by a Coach was at least as efficacious as support from a Clinical Psychologist. Study 3 examined the effect of the Anxiety Program on comorbidity, using data from the second RCT. This final study revealed that participants with comorbid anxiety or depressive disorders demonstrated at least the same magnitude of change as participants without comorbid disorders, and that treatment significantly reduced the overall severity of comorbid disorders as well as number and type of comorbid disorders. Overall across the two RCTs, encouraging outcomes were observed for participants with the three target disorders, and participants rated the Anxiety Program as highly acceptable. These results indicate that transdiagnostic iCBT interventions have considerable potential in improving access to evidence-based treatment.