Table 1.

Risk of ductal carcinoma in situ of the breast in women participating in the Women’s Health Initiative Calcium Plus Vitamin D trial over the entire follow-up period, overall and after various sensitivity analyses

Study population	Placebo		Calcium plus Vitamin D		HR (95% CI)a	P b
	No. cases	IR/1000	No. cases	IR/1000
Total sample	325	1.16	270	0.95	0.82 (0.70 to 0.96)	.02
Total samplec	325	1.16	270	0.95	0.80 (0.68 to 0.95)	.01
Excluding women with <1 year of follow-up	282	1.11	233	0.90	0.81 (0.68 to 0.97)	.02
Excluding women with previous breast biopsy	255	1.07	185	0.77	0.72 (0.59 to 0.86)	.001
Adherence 50% only	318	1.61	260	1.31	0.82 (0.69 to 0.96)	.02
Adherence 80% only	293	1.31	236	1.06	0.81 (0.68 to 0.96)	.02

^aHazard ratios and 95% confidence intervals were based on Cox proportional hazards models with stratification by age (younger than 60 years, 60 to younger than 70 years, 70 years or older), dietary modification trial participation, hormone replacement treatment trial participation, and prior breast biopsy. CI = confidence interval; HR = hazard ratio; IR/1000 = incidence rate per 1000 person-years.

^bTwo-sided χ² test.

^cAnalysis adjusted for mammogram and clinical breast exam frequency.