R. K. Portenoy, MD, D. Bruns, PsyD, B. Shoemaker, BSN, and S. A. Shoemaker, MD, “Breakthrough pain in community-dwelling patients with cancer pain and noncancer pain, Part 1: Prevalence and characteristics”, J of Opioid Management, vol. 6, no. 2, pp. 97–108, Jan. 2018.