UKSAT.

Methods	Study design: intention to treat Method of randomisation: concealed randomisation using automated telephone/computer Concealment of allocation: unblinded
Participants	Country: United Kingdom Number: 1090 Sex: men (n = 902) and women (n = 188) Age: 60 to 76 years Inclusion criteria: asymptomatic (non‐tender) infrarenal aneurysm. Maximum anteroposterior diameter 4.0 cm to 5.5 cm. Fit for elective surgery.
Interventions	Treatment: surgery, n = 563 of whom 528 had immediate aneurysm repair; 35 had no elective operation due to death, refusal, etc. Control: surveillance, n = 527 of whom 401 had aneurysm repair when they met the criteria listed below. Participants assigned to the immediate‐surgery group received standard open repair within 6 weeks after randomisation, while participants assigned to selective surveillance were followed without repair at similar regular intervals (at minimum once every 6 months), and surgery was performed within 6 weeks if: a) the aneurysm reached 5.5 cm; or b) the aneurysm enlarged by a minimum 1.0 cm in 1 year; or c) the aneurysm became tender or symptomatic.
Outcomes	Primary: survival during mean follow‐up (range 8 to 12 years, mean 10 years) (30‐day surgical mortality) Secondary: healthcare costs
Notes	The Medical Research Council and the British Heart Foundation supported this trial.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Concealed randomisation using automated telephone/computer
Allocation concealment (selection bias)	Unclear risk	Concealment of allocation: unblinded
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Cannot blind participants
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Unlikely given the study outcome (mortality) and low lost‐to‐follow‐up rate. Vital status was assessed using the same methodology for both participants in the immediate‐repair group and participants in the routine ultrasound surveillance group‐‐in case misclassification occurred, this would have been non‐differential and its impact on the study results would be limited.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Unlikely given the study outcome (mortality) and low lost‐to‐follow‐up rate
Selective reporting (reporting bias)	Low risk	Authors published findings on all the study outcomes including the study outcome of this review.
Other bias	Low risk	We did not identify other possible risk of bias.

AAVS: American Association for Vascular Surgery
 SVS: The Society for Vascular Surgery