Health measurement scales [electronic resource] : a practical guide to their development and use / David L. Streiner, Department of Psychiatry, University of Toronto, Ontario, Canada, Department of Psychiatry and Behavioral Neurosciences, Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada, Geoffrey R. Norman, Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada and John Cairney, Department of Family Medicine, McMaster University, Hamilton, Ontario, Canada.