eAppendix 1. Multiple imputation results of life course exposure to cigarette smoking and risk of benign breast disease
aBBD cases Crude Adjusted 95% CI
% RR RR
Maternal smoking during pregnancy
None 14.1 1.0 1.0
Less than one pack per day 17.1 1.2 1.2 0.8 – 1.8
One pack or more per day 23.1 1.6 1.6 1.1 – 2.3
Passive smoking (pack-year-hours) During early childhood (0-6 years old)
0 14.8 1.0 1.0
≤60 18.5 1.2 1.2 0.8 – 1.8
>60 19.7 1.3 1.3 0.8 – 1.9
During late childhood (7-10 years old)
0 15.0 1.0 1.0
≤30 19.9 1.2 1.2 0.8 – 1.8
>30 18.2 1.1 1.1 0.8 – 1.7
During adolescence (11-18 years old)
0 16.8 1.0 1.0
≤40 18.8 1.1 1.1 0.8 – 1.6
>40 18.3 1.1 1.1 0.8 – 1.6
Regular active smoker
No 18.6 1.0 1.0
Ex 19.2 1.0 1.0 0.7 – 1.5
Current 16.3 0.9 1.0 0.7 – 1.5
Age of initiation of regular smoking (years)
Not a regular smoker 18.6 1.0 1.0
< 14 21.8 1.2 1.3 0.9 – 2.0
14 - 19 16.1 0.9 0.9 0.7 – 1.3
20 + 16.6 0.9 1.0 0.5 – 1.9
Duration of regular smoking (years)
0 18.5 1.0 1.0
1-9 22.5 1.2 1.2 0.7 – 1.8
10+ 16.8 0.9 1.0 0.7 – 1.4
Smoking intensity (cigarettes per day)
Not a regular smoker 18.6 1.0 1.0
<20 15.3 0.8 0.9 0.6 – 1.2
20+ 21.7 1.2 1.4 1.0 – 2.0b
Cumulative active smoking (pack-years)
0 18.4 1.0 1.0
0.05-10 20.2 1.1 1.1 0.8 – 1.5
>10 15.8 0.9 1.0 0.7 – 1.5
a SAS 9.2 Proc Mi procedure was employed to generate 5 datasets with complete data for all the female offspring participants (N=962). Variables in the imputation model included benign breast disease (BBD) status, all the prenatal and postnatal smoking exposures, and all the confounders. In the following Proc Mianalyze procedure that combined log-binomial regression analyses results from the 5 datasets, we used all the imputed variables, except for the outcome BBD, for which the original data collected from the interviews was used.
b The confidence interval included 1.0.