1 Department of Primary Care Health Sciences, University of Oxford, Oxford OX2 6GG, UK. Electronic address: trish.greenhalgh@phc.ox.ac.uk.
2 Department of Chemistry and Cooperative Institute for Research in the Environmental Sciences, University of Colorado, Boulder, CO, USA.
3 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA.
4 School of Information and Library Science, University of North Carolina, Chapel Hill, NC, USA.
5 Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada.
6 Department of Medicine, Division of Infectious Diseases and Global Public Health, School of Medicine, University of California, San Diego, La Jolla, CA, USA.