Some reasons to include a control group - Trials tend to be conducted at the best facilities, and they monitor their patients extremely well. Thus, control gro

Some reasons to include a control group - Trials tend to be conducted at the best facilities, and they monitor their patients extremely well. Thus, control groups in a trial tend to have a better outcome than the general population. - Patients included in trials tend to be better informed and better motivated to seek treatment. - When trials are run in a specific location, the patient group may be different than the general population (younger/older, less/more exposure to carcinogens, etc.). Note that all of these are in favor of approval for the experimental drug, and combined with financial interest/pressure from pharmaceutical companies to get approval of a drug, leaving out a control group is a recipe for disaster. The hypothetical case you describe where a cancer ends deadly in an average of 6 months for 90% of the population and is suddenly cured by a miracle treatment simply does not happen (see https://www.cancerresearchuk.org/health-professional/cancer-statistics/survival/all-cancers-combined#heading-One https://www.cancerresearchuk.org/health-professional/cancer-... for some statistics), so you will always need a control group.