An emergency medical services (EMS) researcher is conducting a study in which some patients in need of analgesia are treated with acetaminophen and some are treated with both acetaminophen and ibuprofen. Treatment with acetaminophen alone is the current institutional protocol, so patients in this group are the control group; patients receiving both acetaminophen and ibuprofen are the treatment group. Patients are randomly assigned a group, and neither group of patients knows their group designation. The researcher, however, is aware of which patients belong to which group. Based on this information, which study type is being used?
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