1 Centre for Education and Research on Ageing, Concord Hospital, University of Sydney, Concord, NSW 2139, Australia School of Public Health, University of Sydney, Concord, NSW 2139, Australia University of Sydney Pain Management Research Institute, Royal North Shore Hospital, Australia Tel.: +61 2 97675957; fax: +61 2 97675419. Centre for Education and Research on Ageing, Concord Hospital, University of Sydney, Concord, NSW 2139, Australia.