Carrell, D. S., Albertson-Junkans, L., Ramaprasan, A., Scull, G., Mackwood, M., Johnson, E., Cronkite, D. J., Baer, A., Hansen, K., Green, C. A., Hazlehurst, B. L., Janoff, S. L., Coplan, P. M., DeVeaugh-Geiss, A., Grijalva, C. G., Liang, C., Enger, C. L., Lange, J., Shortreed, S. M., & Von Korff, M. (n.d.). measuring problem prescription opioid use among patients receiving long-term opioid analgesic treatment: development and evaluation of an algorithm for use in EHR and claims data. Journal of drug assessment, 9, 97–105. http://access.bl.uk/ark:/81055/vdc_100105286771.0x000013