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Figure 4. Estimated number of strokes prevented and estimated harms of using aspirin for 10 years in a hypothetical cohort of 1000 women on the basis of age and 10-year stroke risk.

As indicated, the estimated number of strokes avoided varies with 10-year stroke risk. The estimated harms of using aspirin vary with age. Therefore, both 10-year stroke risk and age must be considered when determining whether the potential harms of aspirin use outweigh the potential benefit in terms of strokes prevented. The boldfaced numbers indicate the combinations of 10-year stroke risk and age for which the number of harms (GI bleeding) are greater than the number of strokes prevented*

Variable Estimated Strokes Prevented (per 1000 Women), n
Age 55-59 Years Age 60-69 Years Age 70-79 Years
10-year stroke risk  
1% 1.7 1.7 1.7
2% 3.4 3.4 3.4
3% 5.1 5.1 5.1
4% 6.8 6.8 6.8
5% 8.5 8.5 8.5
6% 10.2 10.2 10.2
7% 11.9 11.9 11.9
8% 13.6 13.6 13.6
9% 15.3 15.3 15.3
10% 17 17 17
11% 18.7 18.7 18.7
12% 20.4 20.4 20.4
13% 22.1 22.1 22.1
14% 23.8 23.8 23.8
15% 25.5 25.5 25.5
16% 27.2 27.2 27.2
17% 28.9 28.9 28.9
18% 30.6 30.6 30.6
19% 32.3 32.3 32.3
20% 34 34 34
  Estimated Harms, n
Type of event  
GI bleeding 4 12 18

* Calculations of estimated benefits and harms rely on assumptions and are by nature somewhat imprecise. Estimates of benefits and harms, especially at the borders of the boldfaced and non-boldfaced areas, should be considered in the full context of clinical decision making and used to stimulate shared decision making. The calculations in the table are based on the following assumptions: that there is a 17% risk reduction of strokes with regular aspirin use3 and that gastrointestinal bleeding includes serious hemorrhage, perforation, or other complications leading to hospitalization or death. Harm of GI bleeding in the table assumes that risk for GI bleeding increases with age and that the women are not taking nonsteroidal anti-inflammatory drugs, do not have upper GI pain, or do not have a history of GI ulcer.2 "Strokes prevented" is the net reduction of strokes, which includes a decrease in ischemic strokes and a small increase in hemorrhagic strokes.

GI = gastrointestinal.

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