Table 6. The incidence rate ratio of osteoporosis or fracture interacts with estrogen treatment.

						IRR (95% CI)
Hysterectomy	Estrogen treatment	N	Event	PY	IR	Crude	p-value	Adjusted*	p-value
			Osteoporosis or bone fracture
No	No	33833	1852	251443	7.37	1.00 (reference)		1.00 (reference)
No	Yes	59	15	450	33.31	4.65 (2.80,7.73)	<0.001	3.49 (2.10,5.81)	<0.001
Yes	No	9151	1043	64012	16.29	2.09 (1.93,2.25)	<0.001	2.05 (1.90,2.21)	<0.001
Yes	Yes	38	6	208	28.85	2.89 (1.30,6.44)	<0.001	2.74 (1.23,6.12)	0.01
			Osteoporosis
No	No	33180	1149	247968	4.63	1.00 (reference)		1.00 (reference)
No	Yes	49	5	398	12.57	2.95 (1.22,7.09)	0.02	2.18 (0.90,5.25)	0.08
Yes	No	8527	419	60769	6.90	1.42 (1.27,1.59)	<0.001	1.41 (1.26,1.58)	<0.001
Yes	Yes	34	2	193	10.36	1.70 (0.42,6.80)	0.45	1.55 (0.39,6.20)	0.54
			Hip fracture
No	No	32111	80	242384	0.33	1.00 (reference)		1.00 (reference)
No	Yes	46	2	374	5.35	17.45 (4.29,70.99)	<0.001	9.59 (2.33,39.58)	0.002
Yes	No	8128	20	58914	0.34	0.99 (0.61,1.61)	0.96	1.01 (0.62,1.64)	0.98
Yes	Yes	32	0	187	0.00	--		--
			Vertebral fracture
No	No	32139	108	242607	0.45	1.00 (reference)		1.00 (reference)
No	Yes	50	6	402	14.94	35.71 (15.7,81.25)	<0.001	26.33 (11.44,60.60)	<0.001
Yes	No	8235	127	59515	2.13	4.59 (3.55,5.93)	<0.001	4.45 (3.44,5.76)	<0.001
Yes	Yes	32	0	187	0.00	--		--
			Other bone fracture
No	No	32556	525	244617	2.15	1.00 (reference)		1.00 (reference)
No	Yes	46	2	369	5.42	2.70 (0.67,10.81)	0.16	2.59 (0.65,10.41)	0.18
Yes	No	8607	499	61372	8.13	3.60 (3.18,4.06)	<0.001	3.53 (3.12,3.99)	<0.001
Yes	Yes	36	4	202	19.81	6.89 (2.58,18.43)	<0.001	6.73 (2.51,18.05)	<0.001

PY: Person-years; IR: Incidence rate per 1,000 person-years; HR: Hazard ratio; CI: Confidence interval.

*: Model was adjusted for age, urbanization, insurance premium, occupation, estrogen treatment, and Charlson comorbidity index.