Abouzari 2009.

Study characteristics
Methods	RCT
Participants	195 people undergoing elective cranial surgery in Iran between March 2005 and December 2007
Interventions	3 preoperative surgical site treatments involving removal, or no removal, of scalp hair: Group 1: removal with a razor (n = 65) Group 2: removal with hair clippers (n = 65) Group 3: no hair removal (n = 65) Product details: no details are given for the razor, the clippers were "barbers clippers". Time of hair removal: no details given. Hair removed by: not specified. Venue for hair removal: not reported.
Outcomes	Outcome: infection. Defined as including presence of pus, bacterial culture, development of postoperative meningitis and microbiology. Participants were followed up at 3 or 4 weekly intervals until complete wound healing or the development of an infection.
Notes	No statistical test of significance used. 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: "Randomly allocated" Comment: no further details given.
Allocation concealment (selection bias)	Unclear risk	No details reported. Comment: not clear whether the person allocating people to groups would have been able to predict the group to which a potential participant would be allocated.
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 be 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 were 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.