The purpose of the famous SHEP study conducted in the late 1980s and early 1990s was "to assess the ability of antihypertensive drug treatment to reduce the risk of nonfatal and fatal (total) stroke in isolated systolic hypertension." Treatment with chlorthalidone was compared with placebo in 4736 patients with hypertension (SHEP, 1991). 2365 received active treatment, 2371 received placebo. The 5-year average systolic blood pressure was 155 mm Hg for the placebo group and 143 mm Hg for the active treatment group, and the 5-year average diastolic blood pressure was 72 and 68 mm Hg, respectively. The 5-year incidence of total stroke was 5.2 per 100 participants for active treatment and 8.2 per 100 for placebo. The relative risk by proportional hazards regression analysis was 0.64 (P = .0003). For the secondary end point of clinical nonfatal myocardial infarction plus coronary death, the relative risk was 0.73. Major cardiovascular events were reduced (relative risk, 0.68). For deaths from all causes, the relative risk was 0.87.

The efficacy of the chlorthalidone intervention was previously calculated and can be best interpreted as:

	A.	The placebo group's risk of stroke was 37% less than the treatment group's risk of stroke.
	B.	The chlorthalidone treatment group's risk of stroke was37% less than the placebo group's risk of stroke.
	C.	We would need to treat 37 people with chlorthalidone to prevent 1 death.
	D.	Subjects treated with chlorthalidone were 3 times less likely to die from a stroke than those who received placebo.

**Previous calculation from previous question: The efficacy of the chlorthalidone intervention for the prevention of stroke may be expressed as: 0.37