Problem: What design is this study? This should be clearly stated. Where is this study on the Levels of Evidence Pyramid? What are the advantages and disadvantages of this research design?
McNicol, E. D., Ferguson, M. C., & Hudcova, J. (2015, June 2). Patient controlled opioid analgesia versus non-patient controlled opioid analgesia for postoperative pain. The Cochrane database of systematic reviews.