A study randomly assigned patients to treatment groups to determine the effect of taking aspirin in preventing the development of colon polyps. One group took an aspirin daily and the other group took a placebo. Neither the patients nor the doctors knew who was getting which pill. This study is best described as a
A) Blinded block design observational study
B) Randomly assigned observational study
C) Block design with random assignment
D) Blind experiment with random assignment
E) Double-blind comparative experiment
Answer: double-blind comparative experiment
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