Gupta 1991.

Methods	Site: Femoral to AK or BK popliteal Study design: single‐centre RCT Method of randomisation: selecting a random card from an unsorted deck of cards marked with the choice of graft material Blinding: unblinded, no documented crossover so as treated/intention to treat analysis not discussed Exclusions post randomisation: none Losses to follow up: none Protocol violations: none
Participants	Country: USA Setting: hospital No. of participants: 122 (59 AK of whom 29 ringed, 63 BK of whom 29 ringed) Age (mean): 71 yrs Sex: split not specified Inclusion criteria: patients without an available ipsilateral ASV long enough to serve as femoro‐popliteal bypass on the basis of a history of prior removal, duplex ultrasonography, saphenous venography or operative findings requiring an AK or BK femoro‐popliteal bypass. Patients whose life expectancy was judged to be less than 3 years were also included whether or not an ipsilateral ASV was available Patients with Rutherford category 1 to 5 ischaemia were eligible, though all but 4 patients had rest pain or tissue loss Exclusion criteria: patients with extensive necrosis requiring sequential grafts to distal arteries, patients requiring bypass for reasons other than arteriosclerotic occlusive disease
Interventions	6 mm ringed or unringed PTFE
Outcomes	Primary patency, secondary patency, limb salvage (secondary patency and limb salvage not presented separately for above and below‐knee grafts so not included)
Notes	Clear anticoagulation and antiplatelet protocol
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomisation by selection of "a random card from an unsorted deck of cards marked with the choice of graft material"
Allocation concealment (selection bias)	Unclear risk	Timing of randomisation not declared
Blinding of participants and personnel (performance bias) All outcomes	High risk	Operative blinding impossible in this type of trial
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Outcome assessors and patients not obviously blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	No losses, clear life table data
Selective reporting (reporting bias)	Low risk	All stated outcomes reported
Other bias	Low risk	Clear anticoagulation and antiplatelet protocol