1. Department of Cardiorespiratory Medicine, Centre for Clinical Sciences, Hull York Medical School, University of Hull , Kingston upon Hull, HU16 5JQ , UK
2. Robertson Centre for Biostatistics and Clinical Trials, University of Glasgow , Glasgow , G12 8QQ, UK
3. Wolfson Palliative Care Research Centre, Hull York Medical School, University of Hull , Kingston upon Hull, HU6 7RX , UK