Conception and design: Kim, Cho, Chung, Oh. Acquisition of data: Kim, Cho, Jeon, Kang, Sohn. Analysis and interpretation of data: Kim, Cho, Chung. Drafting the article: all authors. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Kim. Statistical analysis: Cho, Chung. Study supervision: Kim, Oh.