Table 2 Odds ratio (OR) for endometriosis cases and healthy controls in relation to patient characteristics (predictors).The unadjusted and adjusted OR, with 95 % confidence intervals in brackets, and the corresponding p values are shown.

Predictor	Values	OR unadjusted1	p value	OR adjusted2	p value
1 OR estimated with simple logistic regression models; one model per predictor. 2 OR estimated by a multifactorial logistic regression model with variable selection, as described in the statistical methods section. ORs are adjusted for all other predictors. 3 The predictors age at menarche, number of live births, use of contraceptive pills ever, and body mass index were dropped during the variable selection process.
Age at menarche (years)	≤ 11	1.00 (reference)	–	– 3
	12	0.50 (0.29, 0.89)	0.02
	13	0.63 (0.36, 1.12)	0.12
	14	0.37 (0.21, 0.68)	< 0.01
	≥ 15	0.44 (0.23, 0.87)	0.02
Menstrual cycle length (days)	≤ 27	1.00 (reference)	–	1.00 (reference)	–
	28	0.88 (0.58, 1.34)	0.56	0.71 (0.43, 1.18)	0.19
	≥ 29	1.73 (1.09, 2.75)	0.02	2.33 (1.34, 4.04)	< 0.01
Duration of menstrual bleeding (days)	≤ 4	1.00 (reference)	–	1.00 (reference)	–
	5	0.71 (0.47, 1.10)	0.12	0.84 (0.48, 1.45)	0.53
	≥ 6	1.48 (0.96, 2.29)	0.08	1.86 (1.07, 3.24)	0.03
Number of pregnancies	0	1.00 (reference)	–	1.00 (reference)	–
	1	0.76 (0.49,1.18)	0.21	0.71 (0.40, 1.28)	0.25
	2	0.46 (0.29,0.72)	< 0.001	0.48 (0.27, 0.88)	0.02
	≥ 3	0.30 (0.18,0.49)	< 0.00001	0.17 (0.08, 0.40)	< 0.0001
Number of live births	0	1.00 (reference)	–	– 3
	1	0.61 (0.40,0.93)	0.02
	2	0.45 (0.29,0.70)	< 0.001
	≥ 3	0.30 (0.15,0.60)	< 0.001
Number of miscarriages	0	1.00 (reference)	–	1.00 (reference)	–
	≥ 1	0.87 (0.55,1.38)	0.54	2.76 (1.28, 5.93)	< 0.01
Use of contraceptive pill, ever	no	1.00 (reference)	–	– 3
	yes	0.48 (0.29,0.78)	< 0.01
Body mass index (kg/m2)	≤ 20	1.00 (reference)	–	– 3
	20–25	1.01 (0.60, 1.70)	0.98
	25–30	1.02 (0.55, 1.92)	0.94
	> 30	0.90 (0.39, 2.11)	0.81
Smoking	no	1.00 (reference)	–	1.00 (reference)	–
	yes	2.09 (1.48,2.95)	< 0.0001	2.16 (1.39, 3.36)	< 0.001