Powis 1976.

Study characteristics
Methods	QRCT
Participants	92 people undergoing general surgery in England. Dates not given. Operations include; cholecystectomy, varicose veins, mastectomy, appendicectomy, laparotomy.
Interventions	Group 1: hair removal with a razor (n = 46) Group 2: hair removal with depilatory cream (n = 46) Product details: a disposable razor or a safety razor with disposable blades with a wet shave, the cream was Ipso. Timing of hair removal: either on the day of surgery or the day before surgery depending on surgeon preference. Hair removed by: not reported. Venue for hair removal: not reported.
Outcomes	Primary outcome: clinical evidence of wound infection assessed at day 2 and day 5 by an independent observer. Infections were classified by redness, swelling, exudate, and pus. Wound swabs were also taken at the end of the operation. Secondary outcomes: skin bacteria were assessed at the start and at the end of the operation using agar plates. Skin condition was assessed on day 2 and day 5 by an independent observer, and "spontaneous observations by the patients concerning the preparation were encouraged".
Notes	The cream used in the study was supplied by Knox Laboratories Ltd. No details of conflict of interest.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Quote: "Allocated randomly depending on the last digit of their hospital registration number." Comment: non‐random approach.
Allocation concealment (selection bias)	High risk	Quote: "Allocated randomly depending on the last digit of their hospital registration 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	Quote: "Patients allocated to group 1 . . . were then shaved with either a disposable razor or a safety razor. Patients allocated to group 2 received an application of Ipso. . . in accordance with the manufacturer's instructions" Comment: participants would have been aware of hair removal method.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "Independant observer who was unaware of the method of preparation" Comment: consider adequate approach.
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	Low risk	Quote: "A prospective randomised survey was performed in 92 patients" Comment: 92 analysed for wound infection, no dropouts reported.
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.