1. School of Software, Central South University, Changsha, Hunan 410075, P. R. China
2. Department of Computer, Communication and Interactive System, School of Engineering and Built Environment, Glasgow Caledonian University, Glasgow, Lanärkshire G4 0BA, UK
3. Division of Health & Social Care Research, King’s College London, London SE1 1UL, Strand, London WC2R 2LS, UK