About the Authors

Caroline H. D. Jones

caroline.jones@phc.ox.ac.uk

Current address: Department of Primary Care Health Sciences, Oxford, United Kingdom

Affiliation MRC Epidemiology Unit and UKCRC Centre for Diet and Activity Research, University of Cambridge, United Kingdom

Simon Cohn

Affiliation Institute of Public Health, University of Cambridge, Cambridge, United Kingdom

David Ogilvie

Affiliation MRC Epidemiology Unit and UKCRC Centre for Diet and Activity Research, University of Cambridge, United Kingdom

Competing Interests

Two commercial bus operators (Stagecoach and Whippet) provided travel tickets for the fieldworker free of charge. The operators had no input into study design, data analysis, or the decision to submit the work for publication. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials.

Author Contributions

Conceived and designed the experiments: CJ SC DO. Performed the experiments: CJ. Analyzed the data: CJ SC. Wrote the paper: CJ SC DO.