In order to verify the efficacy of a new drug for the treatment of hypertension, clinicians gave the drug to 100 hypertensive patients. 65 people's blood pressure did indeed drop. 
The drug was given to a group of 100 hypertensive patients, and the other group of 100 hypertensive patients were given the same appearance but contains no drug ingredients.The number of blood pressure drops in the first group of patients was as same as that in the latter group.
 the pharmaceutical factory claimed that the drug was indeed effective.