About the Authors

Lina Chen

Affiliation Department of Social Medicine, University of Bristol, Bristol, United Kingdom

George Davey Smith

Affiliation Medical Research Council Centre for Causal Analyses in Translational Epidemiology, University of Bristol, Bristol, United Kingdom

Roger M Harbord

Affiliation Department of Social Medicine, University of Bristol, Bristol, United Kingdom

Sarah J Lewis

To whom correspondence should be addressed. E-mail: s.j.lewis@bristol.ac.uk

Affiliation Department of Social Medicine, University of Bristol, Bristol, United Kingdom

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

LC and SJL designed the study, analyzed the data, and contributed to writing the paper. GDS designed the experiments and contributed to writing the paper. RMH analyzed the data and contributed to writing the paper. Both LC and SJL 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.