About the Authors

Freesia Horsted
Joe West
Matthew J. Grainge

matthew.grainge@nottingham.ac.uk

Affiliation Division of Epidemiology and Public Health, University of Nottingham, Nottingham, United Kingdom

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

Conceived and designed the experiments: JW MJG. Performed the experiments: FH MJG. Analyzed the data: FH MJG. Contributed reagents/materials/analysis tools: JW MJG. Wrote the first draft of the manuscript: FH MJG. Contributed to the writing of the manuscript: FH JW MJG. ICMJE criteria for authorship read and met: FH JW MJG. Agree with manuscript results and conclusions: FH JW MJG. Carried out original literature search: FH. Made decsions over which papers to include in the review: FH JW MJG. This work was originally carried out as a medical student project by FH under the supervision of JW and MJG prior to the search strategy being updated in July 2011.