Accepted for Publication: June 27, 2012.
Author Contributions: All authors had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Li. Acquisition of data: Zuo and Zheng. Drafting of the manuscript: Li, Zuo, and Zheng. Critical revision of the manuscript for important intellectual content: Li. Statistical analysis: Li. Administrative, technical, and material support: Zuo. Study supervision: Li.
Conflict of Interest Disclosures: None reported.