1 National Collaborating Centre for Indicator Development, Primary Care Clinical Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK p.s.gill@bham.ac.uk.
2 National Collaborating Centre for Indicator Development, Primary Care Clinical Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
3 Health Economics Consortium, University of York, York YO10 5DD, UK.