Sickle-cell disease is a painful disorder of the red blood cells. To investigate whether the drug hydroxyurea can reduce the pain associated with sickle-cell disease, a study by NIH gave the drug to...

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Extracted text: Sickle-cell disease is a painful disorder of the red blood cells. To investigate whether the drug hydroxyurea can reduce the pain associated with sickle-cell disease, a study by NIH gave the drug to 150 sickle-cell sufferers and the placebo to another 150. Neither doctors nor patients were told who received the drug. The number of episodes of pain reported by each subject was recorded, This is an example of Select one: 3, a matched pairs experiment. b. an observational study C. a double blind experiment. d.a simgle blind experiment.