About the Authors

Fotini K Kavvoura

Affiliation Clinical and Molecular Epidemiology Unit, Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece

George Liberopoulos

Affiliation Clinical and Molecular Epidemiology Unit, Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece

John P. A Ioannidis

To whom correspondence should be addressed. E-mail: jioannid@cc.uoi.gr

Affiliations Clinical and Molecular Epidemiology Unit, Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece , Department of Medicine, Tufts University School of Medicine, Boston, Massachusetts, United States of America

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

JPAI was responsible for conception and design. FKK performed one round of the data extraction on all studies, and GL and JPAI did the second round of extractions. FKK and JPAI analyzed and interpreted the data, performed statistical analyses, and drafted the article. FKK, GL, and JPAI were responsible for critical revision of the article for important intellectual content and were also responsible for final approval of the article. JPAI obtained funding.