1. Department of Family Medicine (J.-H.P., D.-H.K., M.C.), Korea University Ansan Hospital, Korea University College of Medicine.
2. Department of Biostatistics, College of Medicine, The Catholic University of Korea, Seoul (Y.-G.P., J.-H.J.).
3. Department of Neurology (D.-Y.K.), Korea University Ansan Hospital, Korea University College of Medicine.
4. Department of Statistics and Actuarial Science, Soongsil University, Seoul, Korea (K.H.).