Table 2.

Incidence rate of subarachnoid haemorrhage in first degree relatives of index cases^*

Relationship to index case	Type of hospital ward where cases were identified	No of first degree relatives identified	Mean age at start of follow up‡ (years)	Person years of follow up‡	Incident cases in first degree relatives	Standardised incidence ratio (95% confidence interval)
Child	Any	11 640	20.8	88 989	13	3.5 (2.0-6.0)
	Neurosurgical†	9093	20.6	69 314	12	5.7 (3.3-10.1)
Parent	Any	1720	54.5	10 881	5	2.3 (0.9-5.4)
	Neurosurgical†	1188	56.1	7453	3	2.5 (0.8-7.9)
Sibling	Any	1421	26.2	9063	1	2.0 (0.3-14.0)
	Neurosurgical†	1014	27.7	6528	1	3.3 (0.5-23.5)
Total	Any	14 781	25.3	108 933	19	2.9 (1.9-4.6)
	Neurosurgical†	11 295	25.0	83 295	16	4.5 (2.7-7.3)

^*Person first diagnosed (in calendar time) with subarachnoid haemorrhage in family. 

^‡Relatives contributed person years of follow up from date of admission to hospital of index cases. 

^†Only first degree relatives of index cases admitted to neurosurgery wards included. Among these first degree relatives, incident cases of subarachnoid haemorrhage occurring during follow up were only counted if admitted to a neurosurgery ward.