[1] Veer der Veer Inst Parkinsons & Brain Res, Christchurch, New Zealand
[2] Univ Canterbury, Dept Commun Disorders, Christchurch, New Zealand
[3] Watford & Three Rivers Primary Care Trust, Watford, England
[4] Univ S Australia, Sch Math & Stat, Adelaide, SA, Australia
[5] Univ Washington, Dept Environm & Occupat Hlth Sci, Seattle, WA 98195 USA
[6] Univ Washington, Dept Med, Seattle, WA USA
[7] Univ Washington, Dept Surg, Seattle, WA 98195 USA
[8] Univ Washington, Dept Med, Div Cardiol, Seattle, WA USA
[9] Univ Washington, Appl Phys Lab, Seattle, WA 98105 USA
[10] Christchurch Sch Med & Hlth Sci, Dept Obstet & Gynaecol, Christchurch, New Zealand
[11] Christchurch Sch Med & Hlth Sci, Dept Med, Christchurch, New Zealand