[1] Vet Adm Connecticut Healthcare Syst, Neurosurg Sect, West Haven, CT 06516 USA
[2] Yale Univ, Dept Neurosurg, New Haven, CT 06520 USA
[3] Vet Affairs Pittsburgh Healthcare Syst, Neurosurg Sect, Surg Serv Line, Pittsburgh, PA USA
[4] Univ Pittsburgh, Dept Neurol Surg, Pittsburgh, PA 15260 USA
[5] Univ Pittsburgh, Ctr Res Hlth Care, Pittsburgh, PA 15260 USA
[6] Univ Cincinnati, Med Ctr, Sect Outcomes Res & Decis Sci,Dept Internal Med, Div Gen Internal Med, Cincinnati, OH 45221 USA
[7] Univ Cincinnati, Med Ctr, Inst Hlth Policy & Hlth Serv Res, Ctr Clin Effectiveness, Cincinnati, OH 45221 USA
[8] Vet Affairs Med Ctr, Cincinnati, OH 45267 USA