Table 1.

Baseline characteristics of incident breast cancer cases and the full cohort, by machine type

Characteristic	Hologic				GE
	Cases		Cohort		Cases		Cohort
	N	%	N	%	N	%	N	%
Total	812	100.0	17,970	100.0	176	100.0	3180	100.0
Age at mammogram
40–49	43	5.3	1867	10.4	11	6.2	532	16.7
50–59	200	24.6	4837	26.9	48	27.3	965	30.4
60–69	383	47.2	7563	42.1	81	46.0	1265	39.8
70+	186	22.9	3703	20.6	36	20.5	418	13.1
Mammogram year
2004–2007	60	7.4	695	3.9	42	23.9	571	18.0
2008–2009	284	25.0	5235	29.1	122	69.3	2285	71.9
2010–2011	263	32.4	6605	36.8	12	6.8	300	9.4
2012–2013	205	25.2	5435	30.2	0	0	24	0.8
BMI
24 or less	283	34.8	7020	39.1	74	42.0	1415	44.5
25–29	281	34.6	5871	32.7	62	35.2	1029	32.4
30–34	137	16.9	3081	17.1	26	14.8	489	15.4
35–39	60	7.4	1246	6.9	8	4.6	168	5.3
40+	51	6.3	752	4.2	6	3.4	79	2.5
First-degree family history of breast cancer
No	714	87.9	16,498	91.8	155	88.1	2902	91.3
Yes	98	12.1	1472	8.2	21	11.9	278	8.7
Use of postmenopausal hormonesa
None	550	67.7	12,401	69.0	95	54.0	1886	59.3
Estrogen alone	94	11.6	2095	11.7	26	14.8	460	14.5
Estrogen + progestin	127	15.6	2287	12.7	49	27.8	563	17.7
Other	41	5.1	1187	6.6	6	3.4	271	8.5
Parity
Nulliparous	44	5.4	1087	6.0	17	9.7	247	7.8
Parous	645	79.4	13,959	77.7	127	72.2	2308	72.6
Missing	123	15.2	2924	16.3	32	18.2	625	19.6

^aWithin 5 years prior to mammogram date