Irvin 1977.

Methods	RCT Methods to control for contributory patient factors: "The method of randomisation took into account the type of surgery performed..."
Participants	Age: unknown Gender: unknown Type of incision: Group 1: median 43.2%, paramedian 56.8% Group 2: median 40.6%, paramedian 59.4% Type of surgery: Group 1: emergent 16.8%, palliative 12.6%; biliary 27.4%, peptic ulcer 30.5%, intestinal 25.3%, other 16.8% Group 2: emergent 14.6%, palliative 10.4%; biliary 35.4%, peptic ulcer 25.0%, intestinal 20.8%, other 18.8% Contamination classification of included participants: 163 "clean" wounds, 28 "infected" wounds, not broken down by group Pre‐operative antibiotic use: not described Prognostic patient factors: not reported Inclusion criteria: patients going through exploratory laparotomy through median or paramedian incisions Exclusion criteria: not described
Interventions	Comparisons reported: Group 1 Sutures: polypropylene (monofilament, non‐absorbable), polyester retention sutures Suturing technique: continuous (with interrupted retention sutures) Closure method: layered Group 2: Sutures: stainless steel (monofilament, non‐absorbable) Suturing technique: interrupted, 'figure‐of‐8' Closure method: mass Surgeon characteristics: Group 1: consultant 40.0%, registrar 60.0% Group 2: consultant 43.4%, registrar 56.6%
Outcomes	Incisional hernia: palpable defect in abdominal fascia with straining Follow‐up duration: 6 months Wound dehiscence: no definition provided Wound infection: discharge of pus from wound
Notes	Hernia data excluded from analysis due to inadequate follow‐up duration
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"randomly allocated by drawing a trial card at the end of the abdominal procedure, and the method of randomisation took account of the type of surgery performed…"
Allocation concealment (selection bias)	Unclear risk	"randomly allocated by drawing a trial card at the end of the abdominal procedure, and the method of randomisation took account of the type of surgery performed…"
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Not described
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants accounted for and dropouts adequately explained
Selective reporting (reporting bias)	Low risk	There was no evidence of selective reporting
Other bias	Low risk	The study appears to be free of other sources of bias