Table 4. Risk of vertebral fracture in women with hysterectomy compared with the comparison group stratified by follow-up year.

	Comparison group				Hysterectomy				Crude		Adjusted*
Follow time	N	Event	PY	IR	N	Event	PY	IR	HR (95% CI)	p-value	HR (95% CI)	p-value
<5	32189	54	148499	0.36	8267	59	39044	1.51	4.37 (3.02,6.33)	<0.001	4.33 (2.99,6.28)	<0.001
5–9	32135	47	114049	0.41	8208	49	30847	1.59	4.09 (2.74,6.10)	<0.001	3.89 (2.60,5.82)	<0.001
≧9	32088	13	138354	0.09	8159	19	38228	0.50	5.71 (2.82,11.55)	<0.001	5.42 (2.66,11.01)	<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.