O'Dwyer 1992.

Methods	Two‐centre trial. Generation of allocation: unclear. Allocation concealment: adequate (sealed envelope). Blinding: not performed. Follow‐up: unclear. Drop‐outs: none mentioned. Intention‐to‐treat: not mentioned. Sample size calculations: no.
Participants	Patients having cholecystectomy for symptomatic gallstones. In‐ and exclusion criteria: well described. Comparability groups: well matched.
Interventions	SIC versus OC. SIC: through 6 cm incision, rectus muscle divided. OC: not further described. Antibiotic prophylaxis: not mentioned. Routine operative cholangiography in all patients.
Outcomes	Primary and secondary outcome: not specified. Outcome measures: pulmonary, function tests, analgesia requirements, hospital stay. Duration of follow‐up: hospital stay.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment?	Low risk	A ‐ Adequate
Blinding? All outcomes	High risk
Free of selective reporting?	High risk
Free of other bias?	High risk	short follow‐up (hospital stay)