In the developed world the importance of evidence-based policy is increasingly recognised. Panel studies – a long-term study design where a cross-sectional sample of units is selected and surveyed at regular intervals – are being used to gather information about the same people or...

The majority of the world's poor, by income poverty and multi-dimensional poverty, now live in countries officially classified by the World Bank as middle-income countries. Of course nothing happens when a country crosses a (somewhat) arbitrary threshold in per capita income but it does matter...