[1] Univ Washington, Dept Epidemiol, Seattle, WA 98104 USA
[2] Univ Washington, Dept Radiol, Seattle, WA 98104 USA
[3] Univ Washington, Cost & Outcomes Res Ctr, Seattle, WA 98104 USA
[4] Univ Washington, Harborview Injury Prevent & Res Ctr, Seattle, WA 98104 USA
[5] Univ Washington, Dept Neurol Surg, Seattle, WA 98104 USA