Alexander 1983.

Study characteristics
Methods	RCT
Participants	1013 people having elective, clean surgery in the USA between July 1979 and July 1981. Includes vascular, thoracic, abdominal, gynaecological, and neurosurgical.
Interventions	Group 1: clipping day before surgery (n = 249) Group 2: clipping on the morning of surgery (n = 226) Group 3: shaving with a razor the day before surgery (n = 271) Group 4: shaving with a razor on the morning of surgery (n = 266) Product details: no details are given for the razor or the clippers. Timing of hair removal: either the day of surgery or the day before surgery according to randomisation. Hair removed by: not specified. Venue for hair removal: not reported.
Outcomes	Primary outcome: wound infection defined as "discharge of pus"; assessed by a research nurse at discharge and with follow‐up 30 days after discharge. Secondary outcomes: length of stay and cost.
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)	Low risk	Quote: "Patients were randomised by draw of a card from a sealed envelope" Comment: random sequence generation not described in adequate detail.
Allocation concealment (selection bias)	Low risk	Quote: "Patients were randomised by draw of a card from a sealed envelope" Comment: done
Blinding (performance bias and detection bias) Care providers blinded	Unclear risk	No details reported. Comment: unclear whether care providers were blinded to intervention allocation.
Blinding (performance bias and detection bias) Participants blinded	High risk	No details reported. Comment: participants would have been aware of hair removal method.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No details reported. Comment: unclear whether assessors were blinded to intervention allocation.
Incomplete outcome data (attrition bias) ITT analysis undertaken	Unclear risk	No details 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.