About the Authors

Corresponding Author

asandgre@hsph.harvard.edu

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

AS had full access to all of the data in the study and takes responsibility for the integrity and accuracy of the data. MS and GMC participated in project concept and drafting of the manuscript. PM participated in data acquisition and final revision of the manuscript. BKW built and programmed the Web site and participated in final revision of the manuscript. AS and MBM were responsible for project concept and design, acquisition of data, analysis and interpretation of data, drafting of the manuscript, and critical revision of the manuscript for important intellectual content. MBM supervised the study.