We are conducting a study to determine the effects of drug on hypertension. The arterial blood pressure of a random sample of 12 patients is measured before and after the treatment, the data are showing below:

Patient ID	Before	After
1	140	90
2	120	110
3	120	80
4	105	100
5	100	100
6	120	123
7	160	144
8	111	84
9	98	94
10	90	90
11	102	104
12	98	98

Please conduct a sign test to find out whether the surgery changed the arterial blood pressure.