About the Authors
Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, United Kingdom
Institute for Mathematical Sciences, Imperial College London, London, United Kingdom
The authors have declared that no competing interests exist.
Analyzed the data: TG. Other: Initiated the research, obtained the datasets and wrote the outline of the paper: AG. Programmed and performed the data analysis and wrote the first draft of the paper: TG. Developed the statistical methods for calculating the confidence intervals: PC.