38. Healthcare providers are giving more attention to relieving the pain of cancer patients. An article in the journal Cancer surveyed a number of studies and concluded that controlled-release (CR) morphine tablets, which release the painkiller gradually over time, are more effective than giving standard morphine when the patient needs it. The “methods” section of the article begins: “Only those published studies that were controlled (i.e., randomized, double-blind, and comparative), repeated- dose studies with CR morphine tablets in cancer pain patients were considered for this review” [C. A. Warfield, Controlled-release morphine tablets in patients with chronic cancer pain, Cancer, 82(12) (1998): 2299–2306]. Explain the terms in parentheses to someone who knows nothing about medical trials.