Dr. sullivan is conducting a clinical trial to determine if vitamin xx can improve test performance of students in an introductory college nutrition course. dr. sullivan puts all the students' names in a hat and draws names to determine if they will be placed in the control or the experimental group. the experimental group receives a capsule of vitamin xx and the control group a "sugar pill" that tastes and looks identical to the vitamin xx capsule. neither dr. sullivan nor the participants know who is receiving which treatment. this experiment is best described as