All confidence intervals (CIs)were calculated at the 95% level. STATA statistical software (STATA SE version 13, STATA Corp., TX, USA) was used for all the analyses. The function “xtmelogit”was used for the multilevel analysis. This study was approved by the Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences Institutional Review Board (No. 486 and No. 881).