Table 1.

Malaysian Mammographic Study cohort description by mammography history

Variable	All women		Previous mammogram		First mammogram		P value
	N = 1453		N = 744		N = 709
	N	%	N	%	N	%
Demographics
Age1a[mean, sd]	50.0	7.0	53.0	7.0	48.0	7.0	<0.001
Ethnicity2a
Chinese	1018	70.1	530	71.2	488	68.8	0.194
Indian	223	15.4	117	15.7	106
Malay	160		69	9.3	91	12.8
Others	52	3.5	28	3.8	24	3.4
Education Level2
Primary	90	6.2	34	4.6	56	8.1	0.006
Secondary	728	50.1	366	49.9	362	52.3
Tertiary	608	41.8	334	45.5	274	39.6
Missing	27		10		17
Monthly Income (RM)2
Below 5 k	689	47.4	325	44.1	364	52.1	0.010
5 k to 10 k	470	32.4	260	35.3	210
Above 10 k	277	19.1	152	20.6	125	17.9
Missing	20		10		10
Hormonal
Endogenous
Age at menarche1a[mean, sd]	13.0	1.0	13.0	1.0	13.0	1.0	0.626
Missing	10		5		5
Menopausal status2
Pre/perimenopausal	783	53.9	299	40.2	484	68.6	<0.001
Post-menopausal	667	45.9	445	59.8	222	31.4
Missing	3		0		3
Parity2
Nulliparous	229	15.8	104		125	17.6	0.057
Parous	1224	84.2	640		584	82.4
Age at first live births1a[mean, sd]	28.0	5.0	28.0	5.0	27.0	5.0	0.001
Missing	230		105		125
Exogenous
Oral contraceptive usage status2
Never	1004	69.1	508	68.5	496	70.4	0.435
Ever used	443	30.5	234	31.5	209	29.6
Missing	6		2		4
Hormone replacement therapy
(HRT) status2
Never	1306	89.9	627	84.6	679		<0.001
Ever used	142	9.8	114	15.4	28
Missing	5		3		2
Medical history
Family history of breast cancer2a
No	1301	89.5	646	86.8	655	92.4	<0.001
Yes	152	10.5	98	13.2	54	7.6
Previous breast biopsy status2a
No	1305	89.8	676	91.5	629	89.6	0.224
Yes	136	9.4	63	8.5	73	10.4
Missing	12		5		7
Gynaecological surgery2
No	1143	78.7	578	79.7	565	79.7	0.352
Yes	310	21.3	166	22.3	144	20.3
Sterilisation	103	7.1	52		51	7.2
Oopherectomy	33	2.3	21	2.8	12	1.7
Hysterectomy	82	5.6	40	5.4	42	5.9
Total Hysterectomy/TAHBSO	69	4.8	37		32	4.5
Salpingectomy/salpingostomy	23	1.6	16	2.1	7
Body Mass Index (BMI)2
Underweight	48	3.3	16		32	4.5	0.030
Normal weight	812	55.9	425	57.1	387
Overweight	576	39.6	292		284	40.0
Missing	17		11		6
Diabetes status2
No	1335	91.9	673	91.1	662	93.8	0.050
Yes	110	7.6	66	8.9	44	6.2
Missing	8		5		3
Smoking status2
Never	1312	90.3	671	90.2	641	90.4	0.887
Ever smoked	141	9.7	73	9.8	68	9.6

^aIndicates variables in the Gail Model

¹Indicates continuous variable

²Indicates categorical variable

T-test was used for continuous variables and chi-square test for categorical variables