About the Authors
Department of Epidemiology, University of Michigan, Ann Arbor, Michigan, United States of America
Department of Environmental Health Sciences, University of California, Berkeley, Berkeley, California, United States of America
Telefonica, Catalonia, Spain
The authors have declared that no competing interests exist.
Conceived and designed the experiments: IHS JSK MN JMP SL JNSE. Performed the experiments: IHS JMP JNSE. Analyzed the data: IHS JSK JNSE. Wrote the paper: IHS JSK JMP SL JNSE.