English: This picture is intended to help explain the concept of single-subject design of experiment.
The line is supposed to represent how a participant experienced more normal blood pressure during day 1-30, day 61-90 and day 121-150, during which they were under the drug being tested.
During day 31-60 and day 91-120, however, they were under a placebo and their blood pressure is significantly higher and farther from the normal range.
Researcher can then compare the blood pressure during the "taking drug" period vs the blood pressure during the "placebo" period, in order to decide whether the drug is effective in reducing the participant's blood pressure to a more normal level.
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