Table 2.

Stroke by age, systolic blood pressure, and cholesterol concentration according to treatment with aspirin. Figures are numbers of events/person years at entry in each stratum with rates per 1000 person years in parentheses and relative risks corrected for other risk factors

	Aspirin (only)	Placebo	Relative risk	Interaction P value
Age (years):
45-49	0/1447 (0.0)	1/1502 (0.7)	NA	0.85
50-54	3/1905 (1.6)	0/1899 (0.0)	NA
55-59	4/1663 (2.4)	11/1812 (6.1)	0.40
60-64	7/1811 (3.9)	9/1756 (5.1)	0.99
65-69	4/1279 (3.1)	5/1102 (4.5)	0.59
Systolic blood pressure (mm Hg):
<130	2/2688 (0.7)	6/2687 (2.2)	0.41	0.006
130-145	2/2663 (0.8)	10/2582 (3.9)	0.21
>145	14/2754 (5.1)	10/2802 (3.6)	1.42
Cholesterol concentration (mmol/l):
<5.9	3/2808 (1.1)	12/2837 (4.2)	0.20	0.036
5.9-6.7	7/2674 (2.6)	8/2345 (3.4)	0.90
>6.7	8/2471 (3.2)	6/2748 (2.2)	1.53

NA: no events in one treatment group.