1. Susan Johnston Consultancy Services, PO Box 314, Leichhardt, New South wales, 2040, Australia
2. Centre for Health Economics Research and Evaluation (CHERE), University of Sydney, Sydney, Australia
3. Clinical Research Unit for Anxiety Disorders, Mental Health Services, St Vincent's Hospital, Sydney, Australia
4. National Drug and Alcohol Research Centre, University of New South Wales, Sydney, Australia
5. Royal Prince Alfred Hospital, Honorary Medical Officer, St Vincent's Hospital, Sydney, Australia