A new medicine against hypertension was tested on 18 patients. After 40 days of treatment, the following changes of the diastolic blood pressure were observed.
-5, -1, +2, +8, -25, +1, +5, -12, -16
-9, -8, -18, -5, -22, +4, -21, -15, -11
Use the sign test to determine if the medicine has an effect on blood pressure. What is the p-value?