Table 2.

 Absolute risk of venous thrombosis associated with oral contraceptive use by age category

Age category	Incidence of venous thrombosis in non-users of oral contraceptives (I0) per 10 000 person-years*	Relative risk (95% CI) of oral contraceptive use†	Incidence of venous thrombosis in oral contraceptive users (I1) per 10 000 person-years‡
<30 years	1.2	3.1 (2.2 to 4.6)	3.7
30-40 years	2.0	5.0 (3.8 to 6.5)	10.0
40-50 years	2.3	5.8 (4.6 to 7.3)	13.3

*I₀ is based on incidences published by Naess et al.³⁰

†Non-users of oral contraceptives are used as the reference category.

‡I₁=I₀×relative risk.