Table 2 Randomised aspirin assignment and report of newly diagnosed asthma in the Women’s Health Study (N = 37 270)

	Aspirin group(N = 18 652)(181 467 person years)	Placebo group(N = 18 618)(180 652 person years)	Hazard ratio*(95% CI)	p Value
Newly diagnosed asthma (n)	872	963	0.90 (0.82 to 0.99)	0.027

Stratified analyses
Age (years)				0.37†
<55	550	595	0.92 (0.82 to 1.03)	0.16
55–64.9	249	268	0.92 (0.78 to 1.10)	0.37
65+	73	100	0.73 (0.54 to 0.99)	0.04
Smoking status				0.97†
Never	419	459	0.91 (0.80 to 1.04)	0.16
Past	322	357	0.89 (0.77 to 1.04)	0.13
Current	131	146	0.91 (0.72 to 1.15)	0.44
BMI (kg/m2)				0.002†
<25	336	406	0.83 (0.71 to 0.95)	0.01
25–29.9	258	319	0.80 (0.68 to 0.95)	0.01
30+	265	224	1.19 (0.99 to 1.42)	0.06
Exercise				0.32†
Rarely	347	364	0.95 (0.82 to 1.10)	0.45
<1/week	198	205	1.00 (0.83 to 1.22)	0.97
1–3/week	240	294	0.81 (0.68 to 0.95)	0.01
⩾4/week	87	100	0.84 (0.63 to 1.12)	0.24
Postmenopausal hormone use				0.89†
Never	387	429	0.91 (0.79 to 1.04)	0.16
Past	86	92	0.96 (0.71 to 1.29)	0.77
Current	396	438	0.89 (0.77 to 1.01)	0.08
Vitamin E				0.57†
Active	428	485	0.88 (0.77 to 1.00)	0.05
Placebo	444	478	0.93 (0.81 to 1.05)	0.25

CI, confidence interval; BMI, body mass index
*Calculated from Cox proportional hazard models using the placebo group as reference.
†p Value for modification from contrast of a model that included main effects only with a model that also included interaction term indicators using the likelihood ratio test.