aPain Research, Department of Surgery and Cancer, Imperial College, Chelsea and Westminster Hospital Campus, London, United Kingdom bPopulation Health Science, University of Dundee, Ninewells Hospital and Medical School, Dundee, United Kingdom cUniversity of Sydney Centre for Education and Research on Ageing, Concord Repatriation General Hospital, Concord, Australia Corresponding author. Address: Pain Research, Department of Surgery and Cancer, Imperial College London, Chelsea and Westminster Hospital campus, 369 Fulham Road, London, SW10 9NH UK. Tel.: + 44 208 746 8816. E-mail address: [email protected] (A.S.C. Rice). Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.painjournalonline.com). Received October 13, 2015 Received in revised form November 09, 2015 Accepted November 10, 2015