Loney PL, Chambers LW, Bennett KJ, et al: Critical appraisal of the health research literature: prevalence or incidence of a health problem. Chronic Dis Canada 19, 2000. Available at: http://www.hc-sc.gc.ca/pphb-dgspsp/publicat/cdic-mcc/19-4/e_e.html. Accessed October 27, 2003.