Author contributions
JL and CEC were responsible for the concept and design of the study. JL, JW and JC were involved in data collection. BCT and AC were involved in data analysis. JL, AC, BCT and CEC drafted the manuscript. All authors critically revised the manuscript for important intellectual content. CEC supervised the study. All authors had full access to all the data in the study, and CEC had the final responsibility for the decision to submit for publication.