Court‐Brown 1981.

Study characteristics
Methods	RCT
Participants	418 people undergoing abdominal surgery (except colostomy) in Scotland between November 1977 and October 1978
Interventions	Group 1: hair removal with a razor (n = 137) Group 2: hair removal with depilatory cream (n = 126) Group 3: no hair removal (n = 141) Product details: the razors were disposable safety razors with a wet shave, the cream was Veeto. Timing of hair removal: 18 to 24 hours before elective surgery and within 6 hours before emergency surgery. Hair removed by: not specified. Venue for hair removal: not reported.
Outcomes	Primary outcome: wound infection defined by presence of pus. Wounds were assessed daily whilst in hospital, and at 28 days postoperatively, unclear by whom. Secondary outcome: acceptability of each method based on "information from staff and patients", cost, and infections when hair removed within 6 hours versus 18 to 24 hours.
Notes	No funding sources mentioned. No details of conflict of interest.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "All patients were randomly allocated" Comment: no description provided of generation of randomisation sequence.
Allocation concealment (selection bias)	Unclear risk	Not reported. Comment: not clear whether the person responsible for allocation to groups would have been able to predict to which group a potential participant would be allocated.
Blinding (performance bias and detection bias) Care providers blinded	Unclear risk	Not reported. Comment: unclear whether care providers were blinded to intervention allocation.
Blinding (performance bias and detection bias) Participants blinded	High risk	Not reported. Comment: participants would have been aware of hair removal method.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported. Comment: unclear whether assessors were blinded to intervention allocation.
Incomplete outcome data (attrition bias) ITT analysis undertaken	Unclear risk	Not reported. Comment: no information provided regarding whether participants were analysed in the groups to which they had been allocated.
Incomplete outcome data (attrition bias) Drop out rate acceptable	Low risk	Participants who dropped out are accounted for, and participants are distributed evenly across groups. Comment: the number of dropouts was judged to be unlikely to have altered the result, even in a worst‐case scenario (i.e. assuming that those that dropped out developed an SSI).
Selective reporting (reporting bias)	Low risk	Main outcomes reported. Comment: unlikely to be affected by reporting bias.
Other bias	Low risk	Comment: participant groups were equal or similar.