Table 1 Included studies

Reference	Year of publication	Country	No. of hospitals	No. of records	Inclusion period	Study design
1. Brennan et al25 32	1991	USA	51	30 121	1984	Retrospective record review
2. O’Neil et al23 28	1993	USA	1	3141	1990–1991	Retrospective record review and review of voluntary reporting data
3. Wilson et al3	1995	Australia	28	14 179	1992	Retrospective record review
4. Thomas et al2	2000	USA	28	14 700	1992	Retrospective record review
5. Vincent et al26 33	2001	UK	2	1014	1998	Retrospective record review
6. Davis et al24 30	2002	New Zealand	13	6579	1998	Retrospective record review
7. Baker et al31	2004	Canada	20	3745	2000	Retrospective record review
8. Sari et al29	2006	UK	1	1006	2004	Retrospective record review and review of voluntary reporting data