Seropian 1971.

Study characteristics
Methods	QRCT
Participants	406 people undergoing surgery, excluding endoscopy, fractures, burns, oral surgery, abscesses, proctological and vaginal surgery, in the USA between June 1968 and February 1969
Interventions	Group 1: hair removal with a razor (n = 249) Group 2: hair removal with depilatory cream (n = 157) Product details: no details are given for the razor, the cream consisted of calcium thioglycollate, calcium hydroxide, and strontium hydroxide. Timing of hair removal: not reported. Hair removed by: not reported. Venue for hair removal: not reported.
Outcomes	Outcome: evidence of wound infection as recorded by wound infection control office through case follow‐up and weekly review; no further details given.
Notes	The study was supported by a grant from CIBA Pharmaceutical Company. No details of conflict of interest.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Quote: the method used was "determined arbitrarily by the last digit of the patient's hospital number". Comment: non‐random approach.
Allocation concealment (selection bias)	High risk	Quote: the method used was "determined arbitrarily by the last digit of the patient's hospital number". Comment: the person allocating participants 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 discussion of whether participants were analysed in the groups to which they had been allocated.
Incomplete outcome data (attrition bias) Drop out rate acceptable	High risk	Reasons for dropouts were given, but group sizes appeared to be unequal. Comment: participants were not evenly distributed across groups.
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.