Table 2

Haemorrhage risk of brain arteriovenous malformation during risk and control periods

Scenario	Included individuals, n	Risk period			Control period			Relative risk (95% CI)	Attributable risk per cent, %
Scenario	Included individuals, n	Event	Person-years	Incidence density, %	Event	Person-years	Incidence density, %	Relative risk (95% CI)	Attributable risk per cent, %
I	311	17	229	7.44	305	8523	3.58	2.08 (1.28 to 3.39)	51.88
II	161	17	220	7.73	151	6280	2.40	3.21 (1.95 to 5.31)	68.89
III	186	17	126	13.48	177	2133	8.30	1.62 (0.99 to 2.67)	38.42
IV	106	17	118	14.41	94	1777	5.29	2.72 (1.63 to 4.57)	63.28