Table 2

Imputation of log estradiol using data from the Nurses' Health Study breast cancer nested case-control study^a
Variable	Beta	Standard error	P value

Intercept	2.241	0.085
Case status	0.130	0.048	0.008
Body mass index (postmenopausal)^b	0.0033	0.0003	<0.001
Birth index^c	-0.0021	0.0006	<0.001
Duration of natural menopause	-0.015	0.004	<0.001
Duration of menopause after bilateral oophorectomy	-0.013	0.004	0.004
R²= 0.219

^aBased on 164 cases and 346 controls. ^bDuration postmenopause × average body mass index postmenopause. ^cBirth index = if parous and = 0 if nulliparous where s = parity; t_i= age at ith birth, i = 1, ..., s; t_m= age at menopause; and b_it= 1 if parity is greater than or equal to i at age t and = 0 otherwise.
Rosner et al. Breast Cancer Research 2008 10:R55 doi:10.1186/bcr2110