Table 2.

Risk of bias assessment

Category	Criteria	Study
		Brooks et al (1972)7	Christiaens et al (2002)8	Ferry et al (2004;9 200710)
Defined sample	Description of source of patients, and inclusion and exclusion criteria	Yes	Yes	Yes
Representative sample	Participants selected as consecutive cases	Yes	Not reported	Not reported
Follow-up rate	Outcome data available for at least 80% of participants at one follow-up point	Yes	Yes	57% at 5–7 weeks, but>80% at 8–10 days
Prognosis	Raw data, percentages, survival rates, or continuous outcomes reported	Yes	Yes	Yes