1. West Australian Sleep Disorders Research Institute, Department of Pulmonary Physiology and Sleep Medicine, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia;
2. Centre for Applied Statistics, University of Western Australia, Crawley, Western Australia, Australia;
3. Department of Research, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia;
4. Fraser Health Authority, Surrey, British Columbia, Canada;
5. School of Medicine and Pharmacology, University of Western Australia, Crawley, Western Australia, Australia; and
6. Department of Pathology, Foothills Hospital, and University of Calgary, Calgary, Alberta, Canada