[1] Seoul Natl Univ, Coll Med, Dept Hlth Policy & Management, Seoul 110799, South Korea
[2] Seoul Natl Univ, Med Res Ctr, Inst Hlth Policy & Management, Seoul 110799, South Korea
[3] Univ Michigan, Dept Hlth Management & Policy, Ann Arbor, MI 48109 USA
[4] Univ Michigan, Dept Econ, Ann Arbor, MI 48109 USA
[5] NBER, Ann Arbor, MI USA
[6] Univ N Carolina, Dept Hlth Policy & Management, Chapel Hill, NC USA
[7] Duke Univ, Med Ctr, Dept Med, Ctr Hlth Serv Res Primary Care,Durham Vet Affairs, Durham, NC 27710 USA