Data collection has been the Achilles heel of all research endeavors. Proper data can be hard to find, acquiring it is often prohibitively expensive and cleaning everything up is time-consuming.

Pew Research Center designed this study to assess the current state of online survey sampling methods – both probability-based and opt-in – and determine their accuracy on general population estimates ...

Andrew J Tatem works for the University of Southampton, and is Director of WorldPop. His research on mapping populations has been funded by donors such as the Gates Foundation, Wellcome Trust, GAVI.