Author contributions
Ju Hee Kim, Seung Won Lee, Hey Sung Baek and Man Young Han contributed to conception and design; Seung Won Lee, Dong Gun Yeon, Hye Mi Jee and Man Young Han acquired the data; Man Young Han, Ju Hee Kim, Seung Won Lee, Eun Kyo Ha, Youn Ho Shin, Seoung In Seo, Sun Hee Choi, Myungsoon Seong analyzed and interpreted the data; Ju Hee Kim and Seung Won Lee drafted the article; Dong Keon Yon, Seung Won Lee, Jung Won Yoon, Hyun Jung Shim and Youn Ho Shin critically revised the article and provided important intellectual content; and all authors approved the final version to be published.