1 MRC/CSO Social and Public Health Sciences Unit, School of Health and Well Being, University of Glasgow, Glasgow G12 8TB, UK; Global Health and Ageing Research Unit, Bristol Medical School, University of Bristol, Bristol, UK.
2 Centre for Research on Health and Social Care Management, SDA Bocconi School of Management, Milan, Italy.
3 MRC/CSO Social and Public Health Sciences Unit, School of Health and Well Being, University of Glasgow, Glasgow G12 8TB, UK; Robertson Centre for Biostatistics, School of Health and Well Being, University of Glasgow, Glasgow, UK. Electronic address: rod.taylor@glasgow.ac.uk.